Microsoft finally admits its September update broke File History

On 13 September we wrote that File History had quietly stopped backing up on a lot of PCs and that Microsoft had said nothing about it. That changed on Sunday.

Microsoft has now published the issue, using wording that will sound familiar to anyone who has been staring at the problem for two weeks: after installing the September 2026 security update, "some customers using File History, might be unable to create or update backups." The list of affected updates is longer than anyone expected. Windows 11 26H1 on KB5124012, 25H2 and 24H2 on KB5124008, 23H2 on KB5122880, Windows 10 22H2 and 21H2 on KB5122878, plus the Enterprise LTSC 2019 and 2016 builds on KB5122876 and KB5123099. The symptoms Microsoft lists are the ones people reported: a "Reconnect your drive" message while the drive sits there connected, a "Last Backup" time that never moves, older files showing "No previous version available", and crashes logged against FileHistory.exe and KERNELBASE.dll.

What Microsoft has not published is a fix. The entry says a resolution is coming in a future Windows update, with no date and no workaround, and the emergency update released on 14 September does not address it. Uninstalling the September update does bring File History back, and it is still a poor trade, because that update carries this month's 966 security fixes including two Windows holes already under attack.

So the situation for the next few weeks is that a backup feature built into Windows is not backing anything up, and it is not telling you. Go and check the "Last backup" date yourself rather than trusting the green tick. If it has been frozen since early September, Tendvane's one-click backup will copy Documents, Pictures and Desktop to your external drive today, which at least puts something recent on the disk while Microsoft works on it. Our original report has the background.