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Windows File History Is Failing After September 2026 Updates
Microsoft says the September 2026 Windows security updates can stop File History from creating or updating backups on some PCs. The affected update paths include Windows 10 21H2/22H2 and Windows 11 22H2 through 26H1.
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Key takeaways
- Microsoft says the September 2026 Windows security updates can stop File History from creating or updating backups on some PCs.
- The affected update paths include Windows 10 21H2/22H2 and Windows 11 22H2 through 26H1.
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openai.comCreate a landscape editorial hero image for this Studio Global article: How are Microsoft’s September 2026 cumulative security updates affecting the built-in File History backup feature across supported Windows 1. Article summary: Microsoft has confirmed that September’s cumulative security updates can prevent File History from creating or updating backups on some Windows 10 and Windows 11 devices. Treat File History as unreliable until a successf. Topic tags: general, general web, user generated. Style: premium digital editorial illustration, source-backed research mood, clean composition, high detail, modern web publication hero. Use reference image context only for broad subject, composition, and topical grounding; do not copy the exact image. Avoid: logos, brand marks, copyrighted characters, real person likenesses, fake screenshots, UI text, readable text, watermarks, charts with fa
File History is not merely showing a cosmetic warning on some systems after the September 2026 Windows security updates. Microsoft says affected devices may be unable to create or update backups, which means a connected backup drive should not be assumed to contain a current recoverable copy. 22
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The symptoms to take seriously
Microsoft lists several signs of the regression:
- “Reconnect your drive” appears even though a compatible external drive or network location is connected and working.
- The “Last Backup” timestamp does not advance.
- Previously backed-up files may show “No previous version available.”
- In some cases, Event Viewer can contain crash events referring to
FileHistory.exeandKERNELBASE.dll.20
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The practical implication is simple: a visible drive and a familiar File History folder do not prove that a new backup completed. Until a current file can be restored successfully, regard File History as failed or unverified on an affected PC.
Which Windows updates are affected?
Microsoft’s September 8 update documentation identifies the File History issue across these client update paths:
| Windows version | September 2026 update |
|---|---|
| Windows 10 21H2 and 22H2 | KB5122878 |
| Windows 11 22H2 and 23H2 | KB5122880 |
| Windows 11 24H2 and 25H2 | KB5124008 — builds 26100.9445 and 26200.9445 |
| Windows 11 26H1 | KB5124012 — build 28000.2954 |
Microsoft describes the issue as affecting some customers, not every device that receives an update. It matters specifically to people and organizations that use File History, the Control Panel feature that backs up files to an external drive or network location. 22
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Microsoft’s current status
Microsoft has acknowledged the problem in its update documentation and says it is working on a resolution. No published workaround is listed in the notices. 22
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The File History failure arrived amid other September Patch Tuesday regressions. Microsoft released out-of-band updates for Remote Desktop Services instability, including KB5129236 for Windows 10 22H2 and KB5129195 for Windows 11 24H2 and 25H2. Those updates addressed the Remote Desktop issue; they should not be treated as a confirmed File History fix. 3
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What to do right now
For home users
- Do not erase or reinitialize the existing File History drive. A reconnect warning can be false, and old backup data may still be valuable.
- Create a separate copy of important current files immediately. Use another external drive, a network location, cloud storage, or another backup product.
- Test restoration, not just backup status. Restore several noncritical files to a different folder. If version history matters, try restoring an older version as well.
- Record what changed. Note the installed KB number, the displayed Last Backup time, the exact error, and relevant Event Viewer entries before changing File History settings.
For IT teams
- Identify endpoints that use File History and have the affected September updates.
- Treat File History as an unverified backup control wherever timestamps are stale, backup runs fail, or restore versions are unavailable.
- Confirm that an independent backup is current and has passed a restore test.
- Preserve existing File History destinations and collect diagnostic details before performing broad resets, cleanup, or reconfiguration.
- When Microsoft releases a corrective update, test both a newly created backup and restoration of older stored versions in a pilot group before broad deployment.
Should you uninstall KB5124008?
Some users have reported that uninstalling KB5124008 restored File History functionality. That is user-reported mitigation, not Microsoft’s published workaround or a guarantee that rollback will work on every affected device. 27
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Rollback also removes the cumulative security update from the device. For most people, the lower-risk response is to keep the security update installed, establish a separate verified backup immediately, and wait for Microsoft’s correction.
An organization may consider rollback only after documenting the security and recovery tradeoff—such as when File History is the sole available backup and a tested alternative cannot be deployed quickly. If rollback is approved, it should be time-limited, monitored, and followed by reinstallation of a corrected update after validation.
The key backup lesson
A backup is only useful if it can be restored. The September 2026 File History regression is a reminder to verify both sides of the process: confirm that new copies are being created, then restore representative files to prove they are usable. Until that test passes, keep an independent copy of data you cannot afford to lose.
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What is the short answer to "Windows File History Is Failing After September 2026 Updates"?
Microsoft says the September 2026 Windows security updates can stop File History from creating or updating backups on some PCs.
What are the key points to validate first?
Microsoft says the September 2026 Windows security updates can stop File History from creating or updating backups on some PCs. The affected update paths include Windows 10 21H2/22H2 and Windows 11 22H2 through 26H1.