KB5078129: This out-of-band update includes fixes and improvements

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

This out-of-band update includes fixes and improvements that are a part of the following updates:

• January 13, 2026—KB5073724 (OS Builds 19045.6809 and 19044.6809)
• January 17, 2026—KB5077796 (OS Builds 19045.6811 and 19044.6811) Out-of-band

The following is a summary of the key issues that this update addresses when you install this update. The bold text within the brackets indicates the item or area of the change we are documenting.

• [File System] Fixed: After installing the Windows update released on and after January 13, 2026, some applications became unresponsive or encountered unexpected errors when opening files from or saving files to cloud-based storage, such as OneDrive or Dropbox. In certain Outlook configurations that store PST files on OneDrive, Outlook may hang and fail to reopen unless the process is terminated or the system is restarted. Users may also see missing sent Items or previously downloaded emails being re‑downloaded.

If you installed earlier updates, only the new updates contained in this package will be downloaded and installed on your device.