Hi @Dr Dave H
Most issues discovered with the Microsoft Teams client can be traced back to firewall or proxy connectivity. Verifying that the necessary URLs, IP addresses and ports are opened in your firewall or proxy will minimize unnecessary troubleshooting. For specific information on URLs and IPs required for Microsoft Teams, please see the Microsoft 365 and Office 365 URLs and IP Address support article.
Additionally, please try clearing the Teams client cache and logging in again to see if the issue is resolved:
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