Duplicate messages posted by 'Unknown User' in Teams

Hi @Sian,

If you are using Teams on the web, you can try clearing the browser cache by following these steps:

Step 1: Press Ctrl + Shift + Delete

Step 2: Select Clear now to remove the data

As for removing the guest and adding them again, you can still do this normally without any impact.

Additionally, I’d like to share one more piece of information: For Microsoft Teams, even if you are using a Business Basic license, you can still use the Teams desktop app.

Hi @Sian,

Welcome to the Microsoft Q&A forum.

I would like to provide you with the following information:

Based on your description, the issue where users are displayed as “Unknown User” along with duplicate messages is commonly related to a data synchronization problem between the application cache and the Microsoft Entra ID directory service.

Please follow the steps below and check whether the issue is resolved:

First, please verify whether the affected user experiences the same issue when using Microsoft Teams on the web.

1. Ask the user to clear the Microsoft Teams cache

To clear the Teams cache, please follow these steps:

• Step 1: Completely exit Microsoft Teams
• Step 2: Press Windows + R, then enter the following path: %userprofile%\AppData\Local\Packages\MSTeams_8wekyb3d8bbwe\LocalCache\Microsoft\MSTeams
• Step 3: Delete all files in this folder
• Step 4: Reopen Microsoft Teams and check the issue again

2. Remove the guest user and add the guest again

You can try removing the guest account and then adding the guest again to check whether the issue still occurs.

If the steps above do not resolve the issue, I recommend creating a support ticket with Microsoft Technical Support for further investigation.

At that point, the support agent will collect logs and analyze the root cause of why the user is displayed as Unknown User, as well as why messages are being duplicated. (These actions do not affect or violate your personal data.)

How to create a Microsoft support ticket:

• Step 1: Go to admin.microsoft.com
• Step 2: Select Help & Support
• Step 3: Enter the title: Request support to investigate Microsoft Teams
• Step 4: Select Contact Support
• Step 5: Choose your preferred contact method

After the system accepts the ticket and assigns a support agent, the agent will proactively contact you and provide assistance.

 I hope this information is helpful. Please follow these steps and let me know if it works for you. If not, we can work together to resolve this.   

Thank you for your patience and your understanding. If you have any questions or need further assistance, please feel free to share them in the comments on this post so I can continue to support you.

I look forward to continuing the conversation.

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