Windows 11 Users Hit by Boot Failures After January 2026 Updates — Microsoft Links Issue to December 2025 Rollback Glitch

In a concerning turn of events for Windows 11 users, Microsoft has confirmed that a wave of boot failures plaguing systems after the installation of January 2026 updates is directly tied to an earlier hiccup involving the December 2025 security patch. The tech giant says devices affected by the recent boot errors were previously unable to install the December update, leaving them in what Microsoft describes as an “improper state.”

The Problem Unfolds

The issue first came to light earlier this month when users running Windows 11 versions 25H2 and 24H2 reported that their systems refused to start after installing the January 2026 Patch Tuesday cumulative update, KB5074109. Instead of booting normally, affected machines displayed the dreaded Blue Screen of Death (BSOD) with the stop error code “UNMOUNTABLE_BOOT_VOLUME,” effectively rendering them unusable.

Microsoft’s Investigation Reveals the Root Cause

Microsoft has since launched a detailed investigation into the matter. According to the company, the boot failures are not random but are linked to devices that previously failed to install the December 2025 security update. When the failed update was rolled back, Windows was left in an unstable or “improper state.”

In an updated advisory first spotted by Susan Bradley of AskWoody, Microsoft explained:

“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.”

The company is now working on a partial resolution designed to prevent additional devices from entering a no-boot scenario if they attempt to install an update while in this improper state. However, Microsoft clarified that this fix will not address the underlying cause that puts devices into this state in the first place, nor will it repair systems that are already unbootable.

Ongoing Investigation and Scope

Microsoft says it continues to investigate why some devices fail to install Windows updates or end up in this improper state following a rollback. The company has also noted that the issue appears to be limited to physical devices, with no reports of virtual machines being impacted.

BleepingComputer reached out to Microsoft for further clarification and additional details about the issue. We will update this story if we receive a response.

What This Means for Users

For now, Windows 11 users are advised to exercise caution when installing updates, especially if they experienced issues with the December 2025 security update. If your system is already unbootable, Microsoft’s partial fix may not help, and more comprehensive solutions may be needed.

This incident highlights the delicate balance Microsoft must strike in delivering timely security updates while ensuring system stability. As Windows 11 continues to evolve, users will be watching closely to see how the company addresses these underlying issues to prevent future disruptions.

Tags: Windows 11, boot failure, BSOD, UNMOUNTABLE_BOOT_VOLUME, January 2026 update, December 2025 security update, Microsoft, Patch Tuesday, KB5074109, improper state, system rollback, Windows update issues, tech news, cybersecurity, operating system bugs.

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