Microsoft Links Windows 11 Boot Failures to Dec 2025 Update
⚠️ Microsoft says recent Windows 11 boot failures following the January 2026 cumulative update are tied to earlier failed attempts to install the December 2025 security update, which left some systems in an "improper state." After applying KB5074109, affected devices showed a BSOD with stop error UNMOUNTABLE_BOOT_VOLUME. Microsoft is working on a partial resolution to prevent new no-boot cases, but it warns this fix will not repair devices already unable to boot or stop systems from entering the improper state. The company also says the issue appears limited to physical machines.
