Microsoft has fixed a known issue that breaks the built-in File History backup feature on some Windows systems after installing the September 2026 security updates.
File History, introduced in Windows 8 and later replaced by Windows Backup, automatically backs up the user's account profile (Documents, Music, Pictures, Videos, and Desktop) to an external hard drive, such as a USB flash drive, or a network storage location (NAS) and then lets them restore accidentally deleted or damaged files using an older version from hours, days, or weeks ago.
In a Saturday service alert seen by BleepingComputer, Microsoft warned that the automated backup feature might stop working after installing this month's security updates and triggering application crash events in Event Viewer referencing FileHistory.exe and KERNELBASE.dll.
On impacted systems running Windows 10 21H2 or later, Windows 10 Enterprise LTSC 2016/2019, and Windows 11 23H2 and later, users are also seeing "Reconnect your drive" alerts even though compatible backup drives are connected and working properly.
Other symptoms include previously backed-up files showing "No previous version available" and the "Last Backup" timestamp not updating.
"After installing the September 2026 Windows security update [..], some customers using File History, might be unable to create or update backups," Microsoft said. "File History, available through Control Panel > System and Security > File History, is used to back up files to an external drive or network location."