Desktop app restarting itself even when on calls

Can you try the following: 

Fully exit Microsoft Teams Client.  (Right click on Teams icon from the icon tray and select "quit", or you can use task manager 😉)

Next, run the following Powershell commands:

Remove-Item –path $env:APPDATA”\Microsoft\teams\blob_storage\*”

Remove-Item –path $env:APPDATA”\Microsoft\teams\Cache\*”

Remove-Item –path $env:APPDATA”\Microsoft\teams\databases\*”

Remove-Item –path $env:APPDATA”\Microsoft\teams\GPUcache\*”

Remove-Item –path $env:APPDATA”\Microsoft\teams\IndexedDB\*” -recurse

Remove-Item –path $env:APPDATA”\Microsoft\teams\Local Storage\*” -recurse

Remove-Item –path $env:APPDATA”\Microsoft\teams\tmp\*”

Restart Teams and see if problems are fixed. 

Let me know!