"Microsoft is investigating reports that its January 2026 security updates are leaving some Windows 11 machines stuck in a boot loop, adding another entry to this month's bumper post-Patch Tuesday borkage list. The issue affects a "limited number" of physical Windows 11 devices that fail to start after installing the January security updates and later patches, instead showing an "UNMOUNTABLE_BOOT_VOLUME" stop code and a black screen offering little more than a restart prompt."
"According to Redmond's own incident note, the problem has been observed on Windows 11 versions 24H2 and 25H2, with no server editions affected and no reports of the same behavior on virtual machines. The first signs of trouble appeared in user forums, where people reported that machines which had been working fine suddenly wouldn't boot after the January updates were installed."
Microsoft is investigating reports that January 2026 security updates are causing some Windows 11 machines to enter a boot loop. A limited number of physical Windows 11 devices fail to start after installing the January updates and later patches, displaying an UNMOUNTABLE_BOOT_VOLUME stop code and a black screen with only a restart prompt. The failures have been observed on Windows 11 versions 24H2 and 25H2; server editions and virtual machines appear unaffected. Affected users reported sudden boot failures in forums, forcing downtime and hands-on recovery instead of routine reboots. Microsoft has received a small number of reports and advises affected customers to contact support or use the Feedback Hub while documentation is updated.
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