Microsoft has confirmed that recent Windows 11 boot failures linked to the January 2026 updates are caused by earlier failed attempts to install the December 2025 security patch.
The issue surfaced after users installed the January 2026 Patch Tuesday update KB5074109 on Windows 11 versions 24H2 and 25H2. Affected systems failed to boot and showed a blue screen error with the stop code UNMOUNTABLE_BOOT_VOLUME.
According to Microsoft, devices impacted by the problem had previously failed to install the December 2025 security update. When Windows rolled back the failed installation, some systems were left in what Microsoft calls an “improper state,” making them unstable.
Microsoft warns that installing new updates while a device is in this improper state can lead to a complete boot failure. The company is working on a partial fix to prevent additional systems from becoming unbootable, but it will not repair devices that are already affected or stop the issue from occurring during failed updates.
The problem currently affects only physical devices, and Microsoft says there are no reports of virtual machines being impacted. The company is still investigating why some systems fail to install updates or end up unstable after rollbacks.
If this article helped you, please consider supporting our work. Every small contribution keeps Abijita.com independent and running.
