Hi there, you need to have your group admins associated with an access levels that allows for this. Even if they are listed as a Group Administrator (vs. a Member) in the Group Members tab when in a Group, that is different from the users' access level in their profile. Go to the access level you have your group admins on (must be Plan license at least) and go to the Users area of the access level > edit > User Admin (Group Users):
If this helped you, please mark correct to help others : )