Microsoft is investigating stories that some Home windows 11 gadgets are failing in addition with “UNMOUNTABLE_BOOT_VOLUME” errors after putting in the January 2026 Patch Tuesday safety updates.
The difficulty impacts Home windows 11 model 25H2 and all editions of Home windows 11 model 24H2 after putting in the KB5074109 cumulative replace launched as a part of this month’s updates.
Based on Microsoft, some prospects have reported that their methods fail to begin and show a cease error throughout boot.
“Microsoft has obtained a restricted variety of stories of a difficulty wherein gadgets are failing in addition with cease code ‘UNMOUNTABLE_BOOT_VOLUME’, after putting in the January 2026 Home windows safety replace (the Originating KBs listed above), launched January 13, 2026, and later updates,” Microsoft acknowledged.
The corporate says that affected gadgets will present a black Home windows crash display stating, “Your machine bumped into an issue and wishes a restart. You may restart.”
Microsoft says the reported methods are unable in addition into Home windows and require handbook restoration efforts in addition once more.
Solely bodily gadgets are reported as impacted by the bug, with no digital machines reported thus far.
Microsoft is asking affected customers and directors to submit suggestions by way of the Suggestions Hub app.
Microsoft says it’s investigating whether or not the conduct is linked to a Home windows replace.
“We’re investigating this subject, and we’ll verify if this can be a regression brought on by a Home windows replace when we’ve additional particulars. We are going to replace this documentation when extra info is confirmed,” Microsoft stated.
Microsoft additionally launched emergency out-of-band (OOB) updates on Saturday to repair a difficulty that prompted Microsoft Outlook to freeze when PST information are saved in cloud companies corresponding to OneDrive or Dropbox.
The corporate stated this subject primarily impacts the Outlook class, which is often utilized in enterprise environments.
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