I somhow solved it, of course right after posting.
Apperently there was a role problem. After i created a new role without an underscore it worked (e.g. superuser).
I noticed that the selection in UAM always got removed if I clicked on the group, so i created a new role without an underscore and sure enough it worked afterwards.
Maybe that helps someone else or maybe it was just a quirky thing on my end.
