Guest name is not properly rendered in Teams Settings
1) The guest was invited to the group through external federation by email
2) He already has a personal Microsoft Account with the same email
3) Adding him in Microsoft Teams as a team member
4) The user is accepting the invitation from Microsoft Teams, creating his guest account and writing his display name and creating his password
5) The Names are not properly rendered in Teams
If the user clicks on his tenant that is Personal Microsoft Account, the system renders the error and there is no way to come back to another, functional Microsoft Teams tenant. The only way to come back to functional tenant is to delete all cookies and click the Teams invitation link from the email.
Shafiq Khan commented
I'm having the same issue ... But mine happens after I invite a guest who is part of another Office 365 Tennant.