How to Fix “Teams Unknown User” Error on Microsoft Teams
To fix the “Teams Unknown User” error, clear the Microsoft Teams cache, sign out the affected user from all devices, and install the latest Windows updates. Restarting your PC may also resolve the issue. The error can occur because of cached data or temporary glitches.
Start by clearing the Teams cache and reopening the app. If the problem persists, sign out the affected user from all devices. These steps can help restore correct usernames and chat information in Microsoft Teams.
What is Microsoft Teams?
Microsoft Teams is a collaborative platform integrated into the Microsoft 365 productivity suite. It offers a comprehensive workspace for team communication, including chat, video conferencing, file sharing, and app integration. The “unknown user” bug issue within Teams is a recognized glitch that can occur for various reasons.
How to Fix This Known Issue: “Teams Unknown Users”
Clear Teams Cache
- Close the Teams apps
- Press Win + R: To open the Run dialog, press the Windows key and “R” simultaneously.
- Type %appdata%\Microsoft\Teams
- Highlight all files and folders inside.
- Press “Shift + Delete” to permanently remove them
or
- Go to C:\Users\<Your staffNumber>\AppData\Roaming\Microsoft\Teams
- Delete all files and folders in the Teams Directory
- Restart Teams.
Sign out the user from all Devices
- Go to Microsoft 365 Admin Center by visiting admin.microsoft.com and logging in with your administrator credentials.
- Left-hand menu, go to “Users” or “Active users.”
- Locate the user you wish to sign out from all devices and select them.
- Sign out the User from all devices in the Account section.
Check Windows Update
- Open Settings.
- Go to Windows Update ( lower left portion of Settings page )
- Make sure that your Windows is up to date. If not.
- Click on Check for updates or Download and Install Updates.
Restart Your Windows PC
Here are the short steps to restart a Windows PC in bullet points:
- Click the Start button
- Select the Power icon
- Click “Restart”
Or, an even shorter version:
- Press Ctrl + Alt + Delete
- Select “Restart”
Frequently Asked Questions
Microsoft Teams may display an unknown user because of cached data, temporary app glitches, or account synchronization issues. Clearing the Teams cache may help resolve the problem.
Clear the Teams cache, sign out the affected user from all devices through the Microsoft 365 Admin Center, install Windows updates, and restart your PC. Check whether the error persists after each step.
Clearing the Teams cache removes temporary files, not your saved chat history or account data. However, close Teams before deleting cache files and avoid deleting unrelated folders.
An update may temporarily cause display or synchronization issues. Restart Teams, check for additional updates, and clear the app cache if the problem continues. If the error persists, contact your Microsoft 365 administrator.
Written by: Menzi Sumile
Reviewed by: Amit
Updated: October 2026
