Seem to be having an issue with DG group owners having ussies managing DG groups post migration specifically adding and removing members
I replicated the issue by adding myself as a manager of said DG and I got the same error
I then tried to check this box in AD on the DG and get the following error
After doing some digging on technet etc its advised to add the "Modify permission" to the group that want to select the option "Manager can update membership list".
As seen here
The option to do this appears greyed out for me, can any of you help with this or any suggestions