This bug is quite similar to
There is some setting which allows moderators to manage groups.
If this is activated, moderators can change the security settings of a groups such that they no longer have access, which is possibly accidental.
Administrators can, of course, recover this situation.
Furthermore, there is an additional odd situation regarding the access of the member list, where Moderators can toggle whether they themselves see the member list.
But maybe that’s not too much of a problem.