A recent Windows update has caused problems for users running Windows 10 ESU (Extended Security Updates) or Enterprise LTSC 2021, including application crashes and freezes when accessing cloud folders like OneDrive. Specifically, Outlook would hang or display a blue screen error when using PST files stored directly within these locations, resulting in lost sent items. Microsoft released an out-of-band patch, KB5078129, to address this issue for ESU and LTSC 2021 builds, specifically version 19044.6812 and build 19045.6812. Installing this update resolves the file-system glitches and brings stability back to affected applications.

KB5078129: Addressing Outlook Hangs and App Instability After the January 13 Windows Update

A recent update on Windows 10 ESU and Windows 10 Enterprise LTSC 2021 has caused some headaches for users. Since its release, several individuals have reported that applications freeze or crash when accessing files in cloud folders like OneDrive. This issue particularly affected Outlook; problems arose when using PST files stored directly within these cloud locations, sometimes leading the program to hang and even displaying a blue screen error alongside lost sent items. Microsoft addressed this problem by bundling fixes into KB5078129. This update was issued as an out-of-band patch specifically for ESU (Extended Security Updates) channels and LTSC 2021 builds, namely version 19044.6812 and build 19045.6812. Installing KB5078129 resolves these file-system glitches, bringing stability back to affected applications.

For more information, check out the Microsoft support article below:

January 24, 2026—KB5078129 (OS Builds 19045.6812 and 19044.6812) Out-of-band - Microsoft Support

January 24, 2026—KB5078129 (OS Builds 19045.6812 and 19044.6812) Out-of-band - Microsoft Support