September 2026 Windows Update: Known Problems and Fixes

September's Windows update has been out for four days. Several things have surfaced. A backup problem, an HP boot failure, AMD graphics cards going haywire, and a support deadline that's easy to miss. Here's what's happening and what you should do.

Microsoft released an emergency fix. Here's what it does and doesn't fix

On 14 September, six days after Patch Tuesday, Microsoft put out KB5129195. It's an out-of-band update, which is their term for one that couldn't wait until next month. They don't do those for fun. When one appears it's because something in the last update broke badly enough that shipping in a hurry beat leaving it four weeks.

It takes Windows 11 to build 26200.9457 on 25H2, or 26100.9457 on 24H2. Mandatory, so Windows Update will fetch it on its own sooner or later. No reason to wait for later.

What it fixes: the Remote Desktop dropouts, the WSL shared folder problem, the multichannel USB audio failures (the 8-channel and 3D surround modes specifically), and a September security fix that turned out to be incomplete, CVE-2026-62721.

What it doesn't fix is the longer list. AMD cards are still crashing. File History is still broken. The domain trust problem further down this page is untouched. If one of those is why you're here, this update won't help you.

How to check whether you've got it

1. Hold the Windows key and press I to open Settings.
2. Click Windows Update at the bottom of the left-hand list.
3. Click Check for updates. If KB5129195 is there, let it install, then restart when it asks.
4. To confirm it went on properly, hold the Windows key and press R, type winver and press Enter. The OS Build line should read 26200.9457 on 25H2, or 26100.9457 on 24H2.

File History backup has stopped working

File History is the backup tool built into Windows. It copies your documents, pictures and desktop files to an external drive on a schedule, so if the laptop dies or you delete something by accident, you can get it back. Since the September updates went on, including KB5124008, a lot of people are finding it simply doesn't run any more.

What they're describing is consistent. The File History panel opens, then throws an error even though the external drive is plugged in and working. The "Last Backup" time sits frozen on a date from days or weeks ago. Nothing new gets copied. There's no crash and no warning box, so unless you go and look, you'd never know.

This one predates September, to be fair. The reports go back to earlier 2026 updates and people had hoped the September cumulative would put it right. It hasn't. KB5124008 goes on and File History stays broken.

Who's affected: people on Windows 10 or Windows 11 who set File History up and rely on it. That's a smaller group than it sounds. File History doesn't switch itself on. Somebody has to plug in an external hard drive and configure it through Control Panel, which most home users have never done. If that's never been you, this isn't your problem and you can skip to the next section.

If it is you, and it's been backing up quietly in the background for months, go and check it. That's the trouble with a silent failure. The backup you're counting on may have stopped in March and you wouldn't have noticed until the day you needed it.

How to check if File History is still working

Two minutes, and you'll want your external drive plugged in first.

1. Press the Windows key on your keyboard. It's the key with the four-part flag symbol, usually bottom-left next to the space bar.
2. Type Control Panel and press Enter. The Control Panel window opens.
3. Click System and Security.
4. Click File History.
5. Look at the line that says Last copied files on: followed by a date and time. If that date is recent, you're fine. If it's weeks or months old, or the page is showing an error message instead, File History has stopped running.

No File History option under System and Security? Then it was never set up on this PC, and none of this affects you.

One thing to try while waiting for a fix

People on the Microsoft Community Hub threads are reporting that reselecting the same drive gets it going again. Microsoft hasn't confirmed this and it's not an official fix, so I'd treat it as worth a go rather than a guarantee. It takes a minute and it can't do any harm.

1. Make sure your external drive is plugged in and Windows can see it.
2. Press the Windows key, type Control Panel and press Enter.
3. Click System and Security, then File History.
4. In the menu down the left-hand side, click Select drive.
5. Click your external drive in the list. It'll be the same one that's already selected. Click it anyway.
6. Click OK.
7. Back on the main File History page, click Run now if you can see it, then wait a few minutes and check whether the "Last copied files on" date has updated to today.

Update, 22 September 2026: the fix is out. It's in KB5124010, an optional update Microsoft released on 22 September. To get it, open Settings, click Windows Update, then Advanced options, then Optional updates. Tick KB5124010, click Download and install, and restart when it asks. If you'd rather not bother with optional updates, the same fix becomes mandatory with October's Patch Tuesday on the 13th. Once it's on, run through the check above and make sure the "Last copied files on" date moves.

Windows 11 24H2 stops getting updates on 13 October

Not a bug, this one. A deadline, and it's the sort that goes unnoticed until it's passed.

Windows 11 comes in versions, and 24H2 is one of them. It's not the same thing as Windows 11 itself. Microsoft puts out a new version roughly once a year and supports each one for a fixed stretch, and 24H2's stretch runs out on 13 October 2026. That's 33 days from now. The current version, 25H2, carries on being supported as normal, so this only bites if your PC is still sat on 24H2.

Home and Pro editions are the ones losing support. Enterprise and Education get until October 2027, which is no help to anyone reading this at a kitchen table.

After the 13th, a machine on 24H2 gets no more security patches, no bug fixes, and no time zone updates. The security patches are the part that matters. Criminals watch for versions of Windows that have gone out of support, because every hole found after that date stays open permanently. It's the same reason I've been nagging people off Windows 10 all year.

How to check which version you're on

1. Hold down the Windows key and press the letter I. The Settings window opens.
2. In the list down the left-hand side, click System.
3. Scroll to the bottom of that page and click About.
4. Under the heading Windows specifications, look at the line marked Version. It'll say 24H2, 25H2 or something older.

If it says 25H2, you're already sorted and you can stop reading this section. If it says 24H2, carry on.

How to upgrade to 25H2

It's free, and it's an ordinary Windows update rather than a reinstall. Your files, programs, settings and desktop all stay exactly where they are. Budget 20 to 30 minutes and don't start it ten minutes before you need the laptop.

1. Hold the Windows key and press I to open Settings.
2. Click Windows Update at the bottom of the left-hand list.
3. Click Check for updates.
4. Windows 11, version 25H2 should appear as an available update. Click Download and install.
5. Leave it alone until it asks you to restart, then restart. It'll spend a while on a screen telling you not to turn the PC off. Believe it.

I won't dress this up as an emergency, because it isn't one today. Nothing breaks on 14 October and the PC will keep working. But there are only 33 days in it, and October is exactly the sort of month where a thing like this gets forgotten. Do it this week and stop thinking about it.

HP laptops not starting after the update

Rarer than the File History bug, and far worse when it happens to you. KB5124008 goes on, the laptop restarts, and it doesn't come back. Some people get a black screen with nothing on it at all. Some get an error code, 0xc0430001, with the words "Code Integrity failed to initialize" underneath. Others sit and watch the thing reboot over and over in a loop that never finishes.

All three come back to the same cause: Secure Boot. That's the check your PC runs at power-on to make sure nothing has tampered with the files Windows starts from. Fail that check and the machine won't boot, which is exactly what you'd want it to do if something really had been tampered with. Less helpful when it's a false alarm. The reports point at a file called boot.stl ending up mismatched partway through the update.

It's mostly HP laptops, going by the HP support forums, with a smaller number of other Windows 11 PCs turning up in the same threads. Microsoft hasn't acknowledged it publicly. There is no patch, no official workaround, and nothing from HP either.

What to do if your HP won't start

Turning Secure Boot off in the BIOS is what people on the HP forums are doing to get back into Windows. It works for a lot of them. It also leaves the PC less protected than it should be and Windows 11 is supposed to have it switched on, so treat it as a way to rescue your files rather than a fix.

1. Hold the power button down for ten seconds to turn the laptop fully off.
2. Press the power button, then immediately start tapping the Esc key once a second until a menu appears.
3. Press F10 for BIOS Setup.
4. Look for a tab called Security or Advanced, then Secure Boot Configuration or Boot Options. The wording moves around between HP models, so have a read of what's there rather than expecting an exact match.
5. Set Secure Boot to Disabled.
6. Press F10 to save and exit. The laptop restarts.

If it boots, get your documents and photos onto an external drive or OneDrive straight away, before anything else. Then ring HP support, because it's their hardware and their firmware, and they need to hear how many people this is hitting. Once there's a proper fix, turn Secure Boot back on.

If tapping Esc gets you nowhere, or the BIOS screen won't come up, stop and get someone to look at it in person. Bring it to me or to any decent local repair shop. A laptop that won't boot is recoverable far more often than people assume, and your files are almost certainly still sat on the drive.

AMD graphics cards freezing and black-screening

This one has only surfaced in the last day or so. People with AMD Radeon graphics cards are finding their PC locks up since KB5124008 went on. Sometimes the screen goes black for a few seconds and comes back with a driver timeout message. Sometimes it goes black and stays there. Sometimes the whole machine freezes and the only way out is holding the power button in.

The cards named so far start at the RX 6600 and go all the way up to the RX 9070 XT. That covers most of what AMD has sold to gamers over the past five years, budget cards and expensive ones alike. The reports are scattered across Reddit and the usual tech forums, in separate threads, from people who clearly aren't talking to each other. When strangers describe the same fault the same way, it's usually a real bug rather than a run of bad installs.

It isn't confined to gaming. Plenty of people are seeing it while browsing or just sat on the desktop doing nothing much.

Who's affected: anyone with a mid-range or high-end AMD gaming PC. If your graphics are built into the processor rather than a separate card, this isn't you. Nvidia cards haven't shown up in the reports at all.

Microsoft hasn't said a word about it. No acknowledgement, nothing on the known issues list, no patch. AMD hasn't released a driver for it either.

So I can't give you a fix, and I'm not going to invent one. Uninstalling the update would stop it, and I'd still tell you not to. This is the patch that closes the best part of a thousand security holes, two of which are being used to break into machines right now. A few black screens is the lesser of those two problems by a distance.

If your PC started freezing or blanking out around the same time the update went on, and there's an AMD card in it, you've most likely found your culprit. Check amd.com/support every few days for a new driver, and leave Windows Update switched on so Microsoft's fix reaches you whenever it turns up.

Business PCs losing access to the company network

These next two only affect business PCs that are joined to a company domain. If this is a home machine, or a standalone work laptop that signs in with a Microsoft account, neither of them applies to you and you can skip to the next section.

Domain sign-ins failing where Credential Guard is on

Since KB5124008, some business computers with Credential Guard enabled have lost trust with their company's Active Directory domain. You type your work username and password and get told "The trust relationship between this workstation and the primary domain failed." Cached credentials from before the update will sometimes still let you in, which hides the problem for a while. A freshly built machine, or a first sign-in after the update, fails outright.

Microsoft confirmed it officially on 16 September 2026. The cause is a feature called Machine Identity Isolation, which the update turned on by itself, including on machines where nobody had asked for it. It needs Windows Server 2025 domain infrastructure behind it to work properly. Most businesses haven't got that.

KB5129195 doesn't fix this. Microsoft says a future update will.

The workaround, for whoever handles your IT:

1. Disable Machine Identity Isolation through Intune or Group Policy. Failing that, set MachineIdentityIsolation to 0 in the registry under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa.
2. Restart the device.
3. Open PowerShell as Administrator and run Test-ComputerSecureChannel -Repair -Credential (Get-Credential).
4. Enter domain admin credentials when it prompts you.

Update, 22 September 2026: the fix is out. KB5124010, the optional preview update released on 22 September, resolves the domain trust issue. Install it via Settings > Windows Update > Advanced options > Optional updates, tick KB5124010, click Download and install, then restart. If you've already got the File History fix installed, you're done. It's the same update. If you'd rather wait, the fix arrives automatically with October's Patch Tuesday on the 13th.

If you're not the IT person and your work laptop has stopped accepting your work account since a recent update, tell your IT department. If you run a small business with nobody looking after the IT and this has landed on you, get in touch.

Always On VPN has stopped connecting

Businesses on a corporate VPN with certificate-based authentication, specifically IKEv2 machine-certificate tunnels handed out through Intune or a similar tool, may find those connections stopped working after KB5124008. The tunnel either refuses to connect at all, or drops the moment it establishes.

Consumer VPN apps are fine. NordVPN, ExpressVPN, Mullvad, none of them are affected. This is enterprise Always On VPN, set up by an IT team, and nothing else.

No official fix was available at first, and KB5129195 was listed as not addressing it. That changed. Installing KB5129195 resolves the "port is already opened" error that was preventing connections from establishing. Confirmed by multiple IT teams on the Microsoft Q&A forums.

Update, 20 September 2026: KB5129195 fixes this. Install it via Settings > Windows Update if you haven't already, restart when prompted, and Always On VPN connections should restore on their own.

USB headsets and speakers that have gone silent

This one affects people with USB audio devices: headsets, USB speakers, sound adapters. If your audio plugs into a headphone jack (the round hole, usually green on a desktop), this isn't relevant to you. The problem is specific to devices that connect via USB.

After KB5124008, a category called USB Audio Class 1.0 has stopped working. These are older-spec devices, and a lot of headsets sold over the past decade fall into this class. USB Audio Class 2.0, the newer standard, isn't affected. When the fault hits, Device Manager logs error Code 10 on the device: "This device cannot start." Volume controls stop responding. If your headset has surround sound or multichannel modes, those go as well.

Microsoft confirmed the issue on 11 September 2026. No fix has been released yet.

How to tell if this is what's happened

Plug in your USB audio device and try playing something. Silence where there shouldn't be is the first sign. To confirm it's this bug:

1. Press the Windows key, type Device Manager, and press Enter.
2. In the list, find Sound, video and game controllers. Click the small arrow to its left to expand it.
3. If your USB headset or speakers have a small yellow triangle on their icon, that's the Code 10 error this bug causes.

No yellow triangle? Try the steps below anyway before writing the device off.

What to try while waiting for a fix

Some users have got their audio back by switching the device to 2-channel stereo mode. Microsoft hasn't confirmed this officially, but several people on the community forums have had it work. It's reversible and takes a few minutes.

1. Press the Windows key, type Control Panel, and press Enter.
2. Click Hardware and Sound.
3. Click Sound.
4. The Playback tab should be open. Find your USB headset or speakers in the list. If the device isn't visible, right-click anywhere in the list and tick Show Disabled Devices.
5. Double-click your USB device to open its Properties.
6. Click the Advanced tab.
7. Under Default Format, click the dropdown and choose an option marked 2 channel. Something like 2 channel, 16 bit, 44100 Hz (CD Quality) is fine.
8. Click Apply, then OK.
9. Try playing audio again.

Also worth trying: unplug the device, wait five seconds, and plug it back in. Then check it's set as the default output. Right-click the speaker icon in the bottom-right corner of the taskbar, click Sound settings, and under Output confirm your USB device is selected.

If none of that works, you're waiting on Microsoft. When the fix arrives it'll come through Windows Update automatically.

Update, 19 September 2026: KB5129195, released on the 14th, fixes the multichannel and 3D/8-channel audio mode failures. If your USB audio went because of the surround sound modes, installing that update should sort it. Standard stereo failures on some USB Audio Class 1.0 devices are still under investigation, and Microsoft says those remaining cases haven't been resolved. Either way, check for updates first, then try the 2-channel stereo steps above if you're still getting silence. Microsoft has confirmed the remaining audio fixes won't arrive until October's Patch Tuesday on the 13th.

Remote Desktop connections dropping mid-session

This only matters if you use Windows Remote Desktop. That's the built-in Windows feature where you connect to another PC or server remotely and see its desktop. Press Windows + R, type mstsc, enter the other machine's address. TeamViewer, AnyDesk, and similar third-party tools aren't affected.

For most home users, none of this applies. You'd know if Remote Desktop was part of your setup.

Since KB5124008, Remote Desktop Services have become unreliable on some machines. Connections drop after a few minutes for no clear reason. Some machines get stuck on a "Please wait for the Remote Desktop Configuration" screen at login and never move past it. Once connected, File Explorer and other tools can freeze on the remote machine.

It's hitting dedicated Remote Desktop servers and Azure virtual machines hardest. Someone who occasionally connects one home PC to another is less likely to hit it, though it's not impossible.

Microsoft confirmed the issue on 11 September and lists a workaround: stop and restart the affected server or VM. For an Azure VM, deallocate it fully and start it again rather than a straight restart. This restores access, but the problem may come back. A permanent fix isn't available yet.

Update, 19 September 2026: KB5129195 fully fixes this. On Windows 11 25H2 build 26200.9457 or 24H2 build 26100.9457, the Remote Desktop instability is gone. Check for updates if you haven't recently.

WSL shared folders not working

Developers only. If you don't use Windows Subsystem for Linux, skip this.

After KB5124008, shared folders from the Windows host aren't accessible from inside the WSL environment. They simply don't appear. Microsoft has confirmed the problem. No fix or workaround is available yet. Check the Microsoft Learn known issues page for this update; it'll be updated when something changes.

Update, 19 September 2026: fixed. KB5129195 fully resolves the WSL shared folder issue. Install it via Settings, then Windows Update, if it hasn't arrived on its own already.

The optional preview update you might spot

Separate from all of the above, Microsoft released KB5124010 on 22 September 2026. It's a preview update, which means optional. Windows won't install it by itself. You have to go looking for it.

It takes Windows 11 to build 26200.9550 on 25H2, or 26100.9550 on 24H2. It also fixes the File History backup problem described earlier on this page. Beyond that, what you get: better file previews in File Explorer, the Emoji 17.0 set, some new precision touchpad gestures on laptops, the ability to remap the Copilot key to something you'd actually use, and an option to have apps open maximised. It also removes the PC-to-PC Migration feature from Windows Backup.

If File History is your backup, install it now and stop worrying. Everyone else can leave it alone. The lot of it becomes mandatory with October's Patch Tuesday on the 13th anyway, by which point it'll have been tested by everyone who couldn't wait. If you want the touchpad gestures now, or you just like being early, it's four clicks.

1. Hold the Windows key and press I to open Settings.
2. Click Windows Update at the bottom of the left-hand list.
3. Click Advanced options, then Optional updates.
4. Tick KB5124010 and click Download and install.
5. Restart when it asks.

If you're still on 24H2, this is the last optional preview you'll get. That version reaches end of support on 13 October.

Citrix and FSLogix virtual desktops booting to a black screen

Enterprise IT only, this one. If you're reading this on your own PC at home, there's nothing here for you and the next section is more use.

Since KB5124008 went on, users signing into virtual desktop sessions are landing on a black screen. No taskbar, no icons, nothing to click. The session is up and the profile has mounted, but explorer.exe either never starts or starts and dies within a second or two of sign-in.

The environments named so far are Citrix VDA, FSLogix profile containers, VMware Horizon, and Liquidware ProfileUnity ProfileDisks. Windows 11 24H2 and 25H2 multi-session Enterprise are both affected, so shifting the estate to 25H2 isn't a way out of it.

Citrix have published their own support article, CTX697101, which tells you something about the volume of tickets landing on their desk. Microsoft are investigating but there's no entry on the official known issues list yet. And KB5129195, the out-of-band update that sorted Remote Desktop and WSL, does nothing for this.

So there's no fix, and I'm not going to invent a registry key that makes it go away. If September's update hasn't reached your session hosts yet, put it on one pilot host and sign in as a real user before it goes anywhere near the rest. If it's already out and your users are sat looking at black screens, you're weighing a rollback against a patch that closes the best part of a thousand holes, two of them being exploited right now. That call depends on how exposed those machines are and nobody outside your organisation can make it for you. Keep an eye on CTX697101 in the meantime. Citrix will most likely have something to say before Microsoft do.

Update, 24 September 2026: Microsoft have now acknowledged it, and there's a way round it that doesn't mean pulling the whole update. They've confirmed physical endpoints aren't affected. It's only pooled VDI with profile containers, which matches what everyone was already seeing. The mitigation is a Known Issue Rollback group policy. For Windows 11 26H1 hosts, deploy KIR policy KB5124006 (policy ID 260924_20071). For 24H2 and 25H2 hosts it's KB5124010 (policy ID 260924_20021). Both need a restart of the session hosts before they take effect. KIR switches off the specific change that's killing Explorer and leaves the security fixes in place, so you keep the protection. It isn't the permanent fix, though. That hasn't shipped yet, and once it does you'll want to remove the policy. For anyone sat on a black screen right now, press Ctrl+Shift+Esc to open Task Manager, click Run new task, type explorer.exe and press Enter. The desktop comes back for that session, which is enough to get them working while the policy rolls out.

Should you still install the update?

Yes. No hesitation on this one.

September's update fixes somewhere between 966 and 974 vulnerabilities, the largest single patch Microsoft has ever shipped, and two of them were already being used to break into machines before the update came out. CVE-2026-81963 and CVE-2026-85880, both privilege escalation flaws rated 7.8. That means an attacker who's got a small foothold on your PC can turn it into total control of the machine. Those are real, in the wild, right now.

None of the problems on this page comes anywhere near justifying skipping that. The 24H2 deadline is a reason to update more, not less. And the File History bug was already there before September, so holding off on the update wouldn't have spared you it.

One caveat if File History is your only backup. It was broken by this month's updates, and KB5129195 didn't help. KB5124010 fixes it, so either install that optional update now or wait for the fix to arrive automatically on 13 October. If you're waiting, copy your important folders to the external drive by hand until then. Lower-tech, but you know it's done.

If something's gone wrong since you installed September's update and you'd rather someone just looked at it, local computer repair is here for the things that need sorting in person.

Three weeks in

Three weeks on and the AMD graphics crashes and HP Secure Boot failure still don't have official fixes, so the workarounds above still apply. USB audio stereo mode is confirmed for October's Patch Tuesday on the 13th, but the AMD GPU fix isn't on that schedule yet. Everything else is sorted: File History and domain trust via KB5124010 on the 22nd, Remote Desktop, WSL, and Always On VPN via KB5129195 on the 14th. I'll update this page if anything changes before October 13.

Mark

Mark has been fixing computers since the late '90s and went self-employed in 2008. Based in St Helens since 2013, he works evenings and weekends from his home in Laffak — friendly, affordable repairs for PCs, laptops, and Macs. See reviews on Google