description: File History backups can stop after the September 2026 Windows 11 update even when the drive is connected. Check the affected builds, the KB5124010 fix and how to protect existing backups.
If Windows 11 started asking you to “Reconnect your drive” after the September 8, 2026 update, your backup disk may be perfectly reachable. Microsoft confirmed that KB5124008 could break File History backups and restores. The problem was fixed in KB5124010, released September 22, and subsequent cumulative updates. Check your Windows build and the last successful backup before changing any backup settings.
What fails, exactly?
Open Control Panel → System and Security → File History. Affected PCs may show a reconnect warning despite a working external drive or network share. The “Last Backup” time can stop advancing, older copies may show “No previous version available,” and Event Viewer may contain crashes involving FileHistory.exe and KERNELBASE.dll. An error banner is annoying; an unnoticed gap in backups is the bigger problem.
Versions and fix
| Windows 11 | Update associated with the issue | Fixed update/build |
|---|---|---|
| 24H2 | KB5124008 / 26100.9445 | KB5124010 / 26100.9550 or later |
| 25H2 | KB5124008 / 26200.9445 | KB5124010 / 26200.9550 or later |
| 26H2 | September update lineage | KB5124010 / 26300.9550 or later |
KB5124010 was a September 22 preview release. As of October 17, 2026, the sensible route is the latest applicable cumulative update offered by Windows Update, which includes earlier fixes. Build numbers are specific to each Windows release.
Check safely, then restore backups
- Press
Win + R, enterwinver, and note your release and build. Look under Settings → Windows Update → Update history for the KB number. - Open the backup drive in File Explorer, or test access to the network share, without deleting or modifying anything. If the destination is genuinely unreachable, inspect the cable, power, or network first.
- Record the last backup date in Control Panel → File History. A date stuck before the update suggests a period without fresh versions.
- Copy irreplaceable current documents and photos to another safe destination. Keep the old File History backup folder and disk intact; do not format the drive or start over just to clear the warning.
- Use Settings → Windows Update → Check for updates. Install the current cumulative update for your version and restart when requested.
- Return to File History, run a manual backup, and verify both the timestamp and an actual backed-up file. If it still fails, save the build number, destination type, and error text for Microsoft Support.
Connection problem or Windows regression?
Microsoft's general reconnect advice is to check the USB drive or reselect the network location. That remains useful when a drive is truly offline. This September bug is different: the destination can be working while File History fails. Users on Microsoft Q&A reported recovery after the September 22 update, but those are individual observations, not a device-wide success rate. Microsoft has confirmed the symptom and fix, not a detailed internal root cause.
Bottom line
Protect existing backup data, install an update containing the KB5124010 fix, and confirm a new backup can actually be restored. A disappearing warning alone is not proof that your files are protected.
