Overview
- Microsoft released out‑of‑band updates, including KB5078127 for Windows 11 24H2/25H2, to fix apps hanging when opening or saving files in cloud locations, which also resolves Outlook freezes with PSTs stored in OneDrive or Dropbox.
- The new fixes are cumulative and incorporate the earlier January 17 emergency patch that addressed shutdown/hibernate failures and Remote Desktop sign‑in problems.
- Microsoft acknowledges a limited number of reports that devices fail to boot with an UNMOUNTABLE_BOOT_VOLUME stop code after installing the January security update KB5074109, with reports affecting physical machines but not virtual machines.
- There is no dedicated fix yet for the boot issue, and affected users may need manual recovery in WinRE or to uninstall the January update using recovery options, according to guidance shared by multiple outlets.
- Admins are advised to deploy the weekend OOB updates where impacted and, if Outlook issues persist, to relocate PST files from cloud‑synced folders or use webmail, noting that uninstalling the security update can increase exposure to vulnerabilities.