You did not respond my second question.
Is it happening with new activities/rooms?
This will help to discard a data conversion problem. If they migrated data, that can be done in too many ways. Depending of the path they followed you could have hit (or not) the bug I was talking about.
Another essential question is always, what version of the BigBlueButtonBN plugin are you using? As I said, there have been some bugs fixed over time.
Lastly, I know I said permissions. My wrong, I shouldn't have used that word. It gets people confused.
I am talking about the participant list inside the Room/Activity.
By default only the user who created the activity/room will be moderator. You can change that manually just to test if that is the problem.