When did this problem happen? What kind of clients have this problem?
How many users in your organization have the same problem?
If it has impact on the majority of your tenant, please contact your IT admin to check if there is any Microsoft Teams relate-advisory of Service health in Microsoft 365 admin center > Health: Service health.
Besides, please try the workaround to change other Teams clients, such as desktop client, web client, mobile client, to have another try.
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