Hi @Klomp, Andy ,
Have you tried to change another browser or desktop client to join class Team?
Does anyone else have the same issue in your organization?
In this case, we firstly recommend you try to delete the cache file to see if it can be fixed, you can navigate to the following location and delete the Teams folder in the Microsoft folder:
C:\Users\username\AppData\Roaming\Microsoft
In addition, The Microsoft Teams app may crash or refuse to open if the Microsoft services are down for maintenance. You can check the status of the service in the admin panel of your Office 365 account.
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