Microsoft’s run of problematic Windows updates shows no sign of coming to an end. The January updates for Windows 11 have already been blamed for a slew of issues, and now there are reports of users being plagued by UNMOUNTABLE_BOOT_VOLUME errors after installation.
The update in question is the KB5074109 update which was release a couple of weeks ago. People affected by this latest problem report the appearance of the error message and a need to restart and perform a system recovery.
Although Microsoft is looking into the problem, the company is yet to update the release notes with a Known Issue. This may change, but at the moment it would seem that not enough is known about the circumstances of the error message appearing to be able to tell if this is a widespread issue or not. There is an acknowledgement of reports of the problem, however in a couple of posts – one for Windows 11, version 25H2 (WI1221934), and one for Windows 11, version 24H2 (WI1221938).
The message Microsoft has posted reads:
Status
Reported
User impact
We are investigating customer reports of device boot failures following the January 2026 update and later updates.
Microsoft has received a limited number of reports of an issue in which devices are failing to boot with stop code “UNMOUNTABLE_BOOT_VOLUME”, after installing the January 2026 Windows security update (KB5074109), released January 13, 2026, and later updates. Affected devices show a black screen with the message “Your device ran into a problem and needs a restart. You can restart.” At this stage, the device cannot complete startup and requires manual recovery steps.
Reports received so far indicate that this issue is limited to physical devices only; no customers have reported observing these symptoms on virtual machines.
If you are experiencing this issue, please contact Support for business [link] or use Feedback Hub to file a report. For additional information, see Send feedback to Microsoft with the Feedback Hub app [link].
Next steps: We are investigating this issue, and we will confirm if this is a regression caused by a Windows update when we have further details. We will update this documentation when more information is confirmed.
Affected platforms:
– Client: Windows 11, version 25H2; Windows 11, version 24H2
– Server: None
It is not clear why Microsoft seems to be having such problems with updates for Windows at the moment. Problematic updates are certainly not unheard of, but in recent times there do seem to have been an incredibly large number of them, calling into question the company’s quality control processes.
Have you been affected by this issue or others caused by Windows updates?
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