Anyone seen this? Groups from trusted domains get a name of "unknown"? Suddenly just happened, no problem adding new groups and/or users, just existing groups.

Not seen that specifically but the web one often shows a SID rather than the group name in certain views, usually the assignment views. Makes it challenging.

Self healed by adding a user from another domain and refreshing... Strange though! 🫣

the SID is translated async in the Web. So the SID is shown when it is not translated fully.