Something in the Teams app, possibly just for Android, doesn't like the inclusion of gcc+commercial accounts. You can do one or the other.
But, this is how I was able to bypass this problem:
- Have commercial account loaded and working
- Select "add account"
- Do not choose your GCC account from the list. Instead select "create or use another account"
- Enter <anything>@contoso.com as the other account.
- When prompted for auth, clear the username, enter your desired GCC username and auth normally.