If File History has told you to “Reconnect your drive” this month while the drive sat plugged in and working, the fix exists, but Windows will not hand it to you yet. Microsoft released it on September 22, 2026 as KB5124010 (builds 26200.9550 and 26100.9550), an optional preview update for Windows 11 25H2 and 24H2, with KB5124006 carrying the same fix for 26H1. Install it now if File History holds the only second copy of your files; otherwise, waiting for October 13, when Patch Tuesday brings it to those versions automatically, costs you little.
The damage came from the September 8 security updates. On 25H2 and 24H2 that was KB5124008; other branches got their own packages, including KB5124012 on 26H1, KB5122880 on Windows 11 23H2, and KB5122878 on Windows 10 22H2 and 21H2. Microsoft’s acknowledgment was blunt: “After installing the September 2026 Windows security update KB5124008, some customers using File History, might be unable to create or update backups.”
The symptoms were easy to miss because nothing looked broken. File History stopped creating or updating backups, the “Last Backup” time froze, and files that had been backed up before could show “No previous version available” under Previous Versions. Event Viewer logged crashes of FileHistory.exe pointing at KERNELBASE.dll. Windows Latest reproduced it on several machines, including a brand-new SSD that behaved normally in File Explorer and third-party apps. Only File History refused to see it.
Two loose ends remain. First, the fixes reported so far name only Windows 11 24H2, 25H2 and 26H1. Tech-Insider says every affected branch, Windows 10 included, was repaired on September 22, while BleepingComputer, PCWorld and Windows Report list no fix outside those three Windows 11 versions. Until Microsoft says otherwise, treat Windows 10 and 23H2 as unconfirmed. Second, Windows Latest and TechRadar report that a separate problem survives KB5124010: pressing “Run now” still fails to update the last-copied time for some users. TechRadar traces that fault to a July update, as does a user report on Microsoft Q&A. KB5124010 restores backups; it does not appear to cure that one.
One overlap matters on 24H2: KB5124010 is the last preview update that version will ever get, because 24H2 Home and Pro stop receiving updates on October 13, the same day the fix arrives automatically on 24H2, 25H2 and 26H1.
Your backups, before and after October 13
Start with one check: open File History and look at the “Last backup” time. If it has not moved since your PC installed the September update, you are affected, and your newest files have no backup copy right now.
On Windows 11 25H2, 24H2 or 26H1, you have two honest options. Install the fix today through Settings, Windows Update: check for updates, then use the “Download and install” link under the optional preview. Or wait, which is what TechRadar recommends, since preview updates are less tested than the Patch Tuesday release that follows them.
Either way, close the gap by hand: copy your Documents, Desktop and Pictures folders onto the backup drive once, so September’s files exist somewhere besides the internal disk. On Windows 10 or 23H2, that manual copy is your safety net until Microsoft confirms a fix for your version.
After October 13, the optional step disappears: the fix installs with the regular update. We follow those updates in our Operating Systems coverage.
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