I reported an issue on the BuddyPress and the Better WP Security plugin support forum that describes how the BuddyPress group admin accounts get lost after executing one of their security features.
There is a feature that renumbers the administrator's account user_id from "1" to something else. I think it's highest user_id+1. In my case it became "5". Consequently, all of my BuddyPress groups lost reference to the admin account.
Details are here.