How to fix your Windows File History if the September update broke it

Microsoft has acknowledged that its September 8 Patch Tuesday security update can break File History in Windows, according to the company's Knowledge Base support pages. Affected users may be unable to create or run backups through File History, and some may see a message telling them to reconnect their drive even when a backup drive is connected and working. The timestamp for the last backup may not refresh, and previously backed-up files may display an error stating that no previous version is available.

All current Windows 11 versions are affected, including 26H1, 25H2, 24H2 and 23H2. Windows 10 is also affected, as users registered for Extended Security Updates continue to receive monthly security updates.

An optional Windows 11 preview update released Tuesday patches the bug. Users must install it themselves through Settings and Windows Update, looking for an update named 2026-09 Preview Update followed by a KB number. The KB number varies by edition: Windows 11 26H1 uses KB5124006, while Windows 11 25H2 and 24H2 use KB5124010. The report says this preview update is the only option for now for users who depend on File History; otherwise, the same fix will arrive with the October Patch Tuesday rollout.

For Windows 11 23H2 and Windows 10, the fix does not apply. Microsoft no longer supports version 23H2, and Windows 10 is supported only through ESU updates. The company says it is working on a fix for those systems that will be released in a future Windows update.

To check whether a machine is affected, users can open Event Viewer by right-clicking the Start button, expanding Windows Logs and selecting Application, then using Filter Current Log with the event level set to Error and the event source set to Application Error, and looking for mentions of FileHistory.exe or KERNELBASE.dll. File History remains supported but is treated by Microsoft as a legacy feature no longer in development; the company directs users to OneDrive or the Windows Backup program for backing up, syncing and recovering files.