We helped a company change their tendant while using the same domain-name. The problem started when we tried to reinviting to the same Team Groups after the migration. We have tried to remove the person from Azure AD guests, wait 24hours and reinviting, and clear cache.
We can still see the company with a red triangle when I try to change account. Having no luck to "reset" and then try it again. It works if I try to invite a new person to the Teams group.