Microsoft Investigates Critical Boot Failures in Windows 11 Version 25H2 After January Update
Microsoft is urgently investigating severe stability issues following the release of the January 2026 security update for Windows 11. The update, designated as KB5074109, was intended to enhance security for Windows 11 versions 25H2 and 24H2. However, it has led to critical boot failures on physical devices, rendering them inoperable.
Critical Boot Failures Confirmed
Users have reported that after installing the January 13, 2026, Patch Tuesday update, their devices enter a boot loop or display a Black Screen of Death. The error message accompanying this issue reads: Your device ran into a problem and needs a restart, with a stop code `0xED` indicating an UNMOUNTABLE_BOOT_VOLUME error. Microsoft has acknowledged these reports, noting that a limited number of devices are unable to complete startup. Interestingly, this problem appears to affect only physical hardware, as virtual machine environments have not exhibited the same defect.
For those affected, the operating system becomes inaccessible, necessitating manual intervention through the Windows Recovery Environment (WinRE) to uninstall the problematic update.
Additional System Stability Issues
Beyond the boot failures, KB5074109 has introduced a range of other system stability problems. Users who can boot their systems have encountered total system lockups and graphics driver conflicts. Notably, GPU-intensive applications like BforArtists 5.0, a Blender fork, experience indefinite hangs when switching viewport shading modes, without triggering a blue screen. These silent lockups are believed to result from conflicts between the new kernel changes and existing DirectX/GPU drivers. Both Nvidia and AMD systems have reported black screens where the Windows user interface fails to render correctly.
Impact on Enterprise Connectivity and Productivity Applications
The repercussions of KB5074109 extend to enterprise environments. Microsoft has confirmed that the update disrupted credential prompts for Azure Virtual Desktop (AVD) and Windows 365, preventing remote connections. This critical flaw was addressed with an out-of-band update, KB5077744, released on January 17.
Additionally, users of Outlook Classic have reported that the application freezes upon launch or fails to sync POP/SMTP accounts due to lingering processes.
Mitigation Strategies
For users encountering the `UNMOUNTABLE_BOOT_VOLUME` error, the recommended course of action is to enter WinRE and uninstall the latest quality update. For those with bootable but unstable systems, Microsoft and security experts advise pausing updates or rolling back KB5074109 through the following steps:
– Navigate to Settings > Windows Update > Update history > Uninstall updates.
Enterprise administrators are encouraged to deploy Known Issue Rollback (KIR) policies where applicable. Consumers are advised to delay the installation of this update until Microsoft releases a comprehensive fix for version 25H2.
