Windows 11 KB5124010 Fixes September File History Backup Bug

Microsoft says the September 22, 2026 Windows 11 preview update KB5124010 fixes a known File History issue introduced by the September security update. The bug could prevent File History from backing up or restoring files to an external drive or network location.

Affected PCs could incorrectly show a “Reconnect your drive” message even when a compatible backup destination was connected and working. Microsoft’s September security-update documentation also lists symptoms including a Last Backup timestamp that might stop updating, missing previous versions, and in some cases FileHistory.exe crashes referencing KERNELBASE.dll.

KB5124010 applies to Windows 11 versions 24H2 and 25H2 and moves them to OS builds 26100.9550 and 26200.9550 respectively. Microsoft classifies it as a non-security preview update and lists the File History correction under the update’s normal-rollout fixes.

Microsoft’s documentation for the September 8 security update KB5124008 now marks the File History problem as resolved in updates released on or after September 22, including KB5124010, and recommends installing the latest Windows update for the device.

File History is designed to preserve versions of user files on an external drive or network location. During the regression, Microsoft says some systems could fail to create or update those backups even though the configured destination remained connected.

The failure could also affect restore confidence: Microsoft documented cases where previously backed-up files displayed “No previous version available.” That makes the issue more consequential than a cosmetic reconnect warning because the visible status could disagree with the expected backup history.

The preview is broader than File History. Microsoft also lists fixes for the built-in camera and several Sysmon problems, alongside gradually rolling out File Explorer and other Windows 11 changes. Those items are separate from the File History regression addressed here.

For File History specifically, the defensible status is that Microsoft marks the September regression resolved by updates released on or after September 22. That does not establish that every unrelated File History failure has the same cause, so systems that still fail after current updates may require separate troubleshooting.