Microsoft's September Update Breaks Windows 11 Backup Feature for Many Users

Microsoft has acknowledged that its September 2026 update for Windows 11 has caused problems with the File History feature. This feature, which is used to back up personal files and folders, stopped working correctly for many users after installing the update. The issue was not immediately noticed by Microsoft, but users who were affected reported that their backups were no longer functioning.

The problem affects users who have installed the Windows 11 KB5124008 update, which rolled out on September 8. This update advances Windows 11 25H2 to Build 26200.9445 and version 24H2 to Build 26100.9445. Users may see a 'Reconnect your drive' alert even when their backup drive is properly connected and functioning.

Microsoft has released an emergency update, KB5129195, on September 14, which fixed some of the issues caused by the initial update, including Remote Desktop problems and Linux-based app crashes. However, File History was still not working correctly. A new optional update, Windows 11 KB5124010, released on September 22, appears to have fixed this issue.