When deleting a group object, ChangeAuditor does not catch the group members being removed from the group. Likewise, when deleting a user, the member of group removed event is also not caught by ChangeAuditor.
It sees that the members and member of attributes cleaned up by Active Directory in the background and thus ChangeAuditor does not catch the event.
Due to the nature of Active Directory object deletion. There is no actual call to remove the user from the group. There is only a deletion, and no removal from the group event.