Summary
- January update triggered UNMOUNTABLE_BOOT_VOLUME BSODs, leaving some Windows 11 PCs unable to boot.
- A failed December update rollback left devices in an improper state, and January’s patch worsened it.
- Microsoft can block further installs but can’t repair already bricked machines; investigation continues.
Windows 11 had a really rough January after Patch Tuesday. We saw some very strange bugs appear over the last month, such as Windows 11 PCs flat-out refusing to shut down when you tell them to. However, among the reports was a bug that seemingly mostly affected commercial PCs, which caused boot issues when using Windows 11.
It’s easy to assume that this was all the fault of a single update, but as it turns out, it goes a bit deeper than that. Microsoft has confirmed that the boot issues are likely due to the January update sitting atop a broken December update, making this more of a chain reaction than a single instance.
Related
Pretty much everything important on Windows 11 has broken, says Microsoft
Not good news for the Redmond giant.
Windows 11’s problems may go deeper than just the January update
A building is only as good as its foundation
As spotted by Bleeping Computer, some Windows 11 computers have been experiencing a nasty boot issue after installing the Windows 11 January update. If affected, the computer will display a “UNMOUNTABLE_BOOT_VOLUME” BSOD error before it can hit the operating system.
Of course, this immediately raised concerns that the January update was the one causing issues, and that’s not entirely wrong. However, as spotted by Susan Bradley of Ask Woody, it turns out that December’s update is also a part of this problem. As Microsoft puts it:
Recent investigations have determined this issue can occur on devices that failed to install the December 2025 security update and were left in an improper state after rolling back the update. Attempting to install Windows updates while in this improper state could result in the device being unable to boot. We are working on a partial resolution that will prevent additional devices from resulting in a no-boot scenario if they try to install an update while in this improper state. However, this partial resolution will not prevent devices from getting into the improper state in the first place, nor will it repair devices that are already unable to boot. We continue to investigate why these devices are failing to install Windows updates or potentially getting into this improper state.
Unfortunately, it seems that Microsoft can only stop devices from installing the update and entering a state where it can enter the BSOD issue. It doesn’t have a fix for computers that have already installed the update, nor is there a fix for people who are experiencing the BSOD issues. There’s a good chance that these January update woes stretch back further than January.