Microsoft has confirmed that Secure Boot certificate updates are failing or being blocked on some Windows 11 PCs.
Microsoft is investigating reports that some Windows 11 devices are failing to boot with "UNMOUNTABLE_BOOT_VOLUME" errors after installing the January 2026 Patch Tuesday security updates. The issue ...
The boot issue, which Microsoft previously investigated and linked to failed December 2025 updates, affected a limited number of commercial Windows 11 devices running versions 25H2 and 24H2.
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