summary
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The January update caused an UNMOUNTABLE_BOOT_VOLUME BSOD that prevented some Windows 11 PCs from booting.
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A failed December update rollback left devices in an inadequate state, and the January patch made the situation even worse.
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Microsoft can block further installations, but cannot repair a machine that has already been bricked. The investigation continues.
Windows 11 had a really tough January after Patch Tuesday. Over the last month, some very strange bugs have appeared: Windows 11 PCs flatly refuse to shut down when you tell them to.. However, the reports also include bugs that appear to primarily affect commercial PCs, causing startup issues when using Windows 11.
It’s easy to attribute this all to one update, but it turns out it’s actually a little deeper than that. Microsoft has acknowledged that the startup issue is likely caused by the January update layered on top of a broken December update, making it likely a chain reaction rather than a single instance.
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as discovered by peepee computerSome Windows 11 computers are experiencing annoying startup issues after installing the Windows 11 January Update. Once affected, the computer will display an “UNMOUNTABLE_BOOT_VOLUME” BSOD error before accessing the operating system.
Of course, this immediately raised concerns that the January update was causing the problem, and that’s not entirely wrong. However, as was discovered, ask woody susan bradleythe December update was also found to be part of this issue. Microsoft says:
Recent research has determined that this issue can occur on devices that failed to install the December 2025 security updates and were left in an incorrect state after the update rollback. If you try to install Windows updates in this incorrect state, your device may become unbootable. We are working on a partial solution to prevent additional devices from running into a no-boot scenario if a device in this improper state attempts to install an update. However, this partial solution does not prevent the device from getting into an improper state in the first place, nor does it repair a device that is already unbootable. We continue to investigate why these devices fail to install Windows updates or may be in this inappropriate state.
Unfortunately, all Microsoft seems to be able to do is prevent devices from installing updates and entering a state that could potentially cause BSOD issues. There is no hotfix for computers that already have the update installed, and no hotfix for users experiencing BSOD issues. It’s entirely possible that these January update issues go back even further than January.