Microsoft patches File History failure caused by September update, but only for Windows 11 so far

FileHistory.exe crashes against KERNELBASE.dll and the backup service goes down with it ^[3]. What the user sees is a prompt to reconnect the backup drive, on a machine where a compatible drive is attached and working normally ^[4]. An admin who trusted that prompt would swap a cable, then a disk, and still have no backups. Two quieter symptoms sit behind it: files already backed up report "No previous version available", and the Last Backup timestamp stops advancing ^[5].

The affected list covers Windows 10 21H2 and later, Windows 10 Enterprise LTSC 2016 and 2019, and Windows 11 23H2 and later ^[4]. Microsoft said on Tuesday that the issue is fixed for Windows 11, and the fix rides in the September 2026 preview update, which is optional ^[7]. For the Windows 10 builds on the affected list, BleepingComputer's report does not identify a preview fix.

The deadline for everyone else is October 13, next month's Patch Tuesday ^[10]. Count back five weeks from that Tuesday and you land on September 8, which was also a Tuesday and the second one in September, so it was September's Patch Tuesday ^[13]. A machine that takes only mandatory updates therefore runs 35 days between break and fix ^[14]. Nothing here is exploitable by an outside party. The loss is recovery: on an affected machine, the newest File History version available to restore predates the September update ^[5].

In Saturday's service alert, Microsoft described the failure itself: after installing the September 2026 Windows security update, it said, some customers using File History might be unable to create or update backups ^[6]. Of the preview update: "This update addresses an issue where File History might fail to back up or restore files to an external drive or network location," Microsoft said ^[8].

This is the fifth distinct regression traced to the September updates in the same reporting ^[15]. A week before the backup alert, Microsoft shipped out-of-band updates for Hyper-V problems, Remote Desktop Services failures and USB audio ^[11]. Days after that, it published a temporary fix for Windows 11 machines refusing valid domain credentials ^[12]. Hyper-V and logon breakage generates a helpdesk ticket the same morning. A stalled backup generates a drive prompt that looks like a hardware fault ^[4].

File History is the older feature, replaced by Windows Backup, and it still runs where someone configured it years ago and stopped looking ^[16]. It writes the account profile folders to an external drive or a NAS ^[2]. Microsoft's guidance on the preview update: "We recommend you install the latest update for your device as it contains important improvements and issue resolutions, including this one," the company said ^[9].