If Windows 11’s File History suddenly stopped backing up your files after the September 2026 update, you’re not imagining it — and it’s not your external drive. Microsoft has confirmed that its own security patch broke the feature, and as of late September the real fix isn’t something Windows installs for you automatically yet.
What’s Actually Broken
After installing KB5124008 (released September 8, 2026, covering Windows 11 25H2 build 26200.9445 and 24H2 build 26100.9445), File History stops reliably creating or updating backups to external and network drives. The symptoms vary but tend to cluster around a few patterns: a “Reconnect your drive” warning shows up even though the drive is plugged in and working, backup timestamps freeze or show the wrong time, clicking “Execute Now” doesn’t actually sync your latest files, and in some cases File History’s background process (FileHistory.exe) crashes outright, leaving matching errors in Event Viewer. Microsoft’s own advisory is blunt about it: “After installing the September 2026 Windows security update KB5124008, some customers using File History, might be unable to create or update backups.”
Why This Happened
This isn’t a settings problem you broke by accident. KB5124008 was a large update — it landed alongside several other regressions that month, including separate issues with Remote Desktop audio, Linux app folder sharing, USB audio, and AMD GPU drivers. File History’s backup engine is what actually got damaged in the process, not your drive, your account, or your existing backup history. Files you backed up before installing KB5124008 aren’t affected; it’s new backups going forward that fail.
The Emergency Patch Didn’t Fix This
Here’s where a lot of people get tripped up: Microsoft did rush out an out-of-band emergency update, KB5129195, on September 14 to deal with the worst of that month’s fallout — but it only addressed Remote Desktop connection failures, a Hyper-V folder-sharing bug, and USB audio problems. It explicitly did not fix File History, and it didn’t touch the AMD GPU issue either. If you installed KB5129195 and backups are still failing, that’s expected, not a sign the patch didn’t work.
The Actual Fix, and Why You Have to Go Get It
The real File History fix shipped on September 23, 2026, as KB5124010 (for 24H2 and 25H2) and KB5124006 (for 26H1) — but both are optional preview updates, meaning Windows Update won’t install them on its own yet. To get the fix now:
- Open Settings > Windows Update > Advanced options > Optional updates.
- Look for KB5124010 (or KB5124006 on Windows 11 26H1) under “Available.”
- Select it, click Download & install, then restart when prompted.
If you’d rather not manually hunt for an optional update, Microsoft has this fix scheduled to fold into the regular October 13, 2026 Patch Tuesday release, at which point it installs the normal way with no extra steps. The tradeoff is simply time: roughly three more weeks of seeing the bug if you wait it out instead of installing the optional update yourself.
What to Do in the Meantime
If you rely on File History for anything you genuinely can’t afford to lose, don’t just wait it out — use OneDrive, or another backup method entirely, as a stopgap until you’ve installed KB5124010 or KB5124006. Uninstalling KB5124008 entirely (Settings > Windows Update > Update history > Uninstall updates) also restores File History, but it removes that month’s security fixes along with it, which isn’t a trade worth making unless you have no other way to back up in the interim.
What Not to Do
Don’t assume your external drive has failed and replace it — this is a confirmed software-side bug, not a hardware fault, and a brand-new drive will hit the identical issue on an affected build. Don’t repeatedly disconnect and reconnect the drive hoping the warning clears, either; it won’t, since the message comes from a broken status check, not the drive itself. And don’t start ignoring every “reconnect your drive” prompt going forward once you’ve installed the fix — that specific false alert should stop, so a genuine one afterward is worth taking seriously again.
Related
Related: For the rest of what KB5124008 broke and fixed, see our full rundown of KB5124008’s known issues, and for what the update was originally meant to change, see our breakdown of the September 2026 Windows 11 update.
FAQ
Does the KB5129195 emergency update fix the File History backup bug?
No. KB5129195 (released September 14, 2026) fixed Remote Desktop, Hyper-V folder sharing, and USB audio issues from that monthu2019s update, but it did not address File History. The actual fix is KB5124010 (24H2/25H2) or KB5124006 (26H1), released September 23, 2026.
Will this bug delete or damage my existing File History backups?
No. Files backed up before installing KB5124008 remain intact. The bug only prevents File History from creating or updating new backups going forward until the fix is installed.
How do I install the File History fix right now instead of waiting?
Go to Settings > Windows Update > Advanced options > Optional updates, and install KB5124010 (or KB5124006 on Windows 11 26H1). Itu2019s optional because Microsoft hasnu2019t pushed it automatically yet u2014 itu2019s scheduled to roll out to everyone with the October 13, 2026 Patch Tuesday update.
Should I uninstall KB5124008 to fix File History?
You can, and it does restore File History, but it also removes that updateu2019s security fixes. Itu2019s only worth doing if you have no other way to back up your files while you wait for KB5124010/KB5124006 or the October Patch Tuesday rollout.