Published 2026-01-28 by TechNet New England
After installing the January 13, 2026 Windows security update (KB5074109), many users experienced a frustrating issue: applications would freeze or become unresponsive when opening files from or saving files to cloud storage like OneDrive or Dropbox.
The problem was especially severe for Outlook users who store PST files on OneDrive. Outlook would hang completely, requiring you to kill the process in Task Manager or restart your computer. Sent emails might not appear in the Sent Items folder, and previously downloaded emails might re-download.
The Fix: Install KB5078127
Microsoft released an emergency out-of-band update on January 24, 2026 to fix this issue.
- Open Settings > Windows Update
- Click "Check for updates"
- Look for KB5078127 (or any later update)
- Install it and restart
If you have "Get the latest updates as soon as they're available" enabled, you should receive this update automatically.
Immediate Workaround: Move PST Files Out of OneDrive
If you can't install the update immediately, moving your Outlook PST files out of OneDrive resolves the issue:
- Close Outlook completely
- Open File Explorer and navigate to your OneDrive folder
- Find your PST files (usually in Documents or a subfolder)
- Move them to a local folder (like C:\Users\YourName\Documents\Outlook Files)
- Open Outlook and go to File > Account Settings > Account Settings
- Click the Data Files tab
- Remove the old OneDrive path and add the new local path
General Cloud Storage Workaround
For other applications having trouble with OneDrive or Dropbox:
- Save files locally first, then copy them to cloud storage
- Pause OneDrive sync temporarily while working on files
- Use the web version of OneDrive for uploads/downloads until you can update
How to Verify the Fix Is Installed
After installing KB5078127 or a later update:
- Go to Settings > Windows Update > Update history
- Look for KB5078127 in the list of installed updates
- Or check Settings > System > About - your build should be 26200.7628 or higher
What Caused This
The January 2026 security update introduced a bug in how Windows handles file operations with cloud-synced folders. The issue affected the Cloud Files Mini Filter Driver, which is responsible for managing files that are stored in the cloud but appear as local files in File Explorer.
When applications tried to open or save files in these cloud-synced locations, the driver would hang, causing the application to freeze.
Microsoft's emergency fix (KB5078127) corrected the driver behavior and restored normal cloud storage functionality.
Having cloud storage or sync issues? Contact TechNet New England for help.