These plugins are fighting with each other.
I had people check my site and they all ended up registering under Membership. NONE ended up registering via BuddyPress so noone showed up as a BuddyPress Member - so no activity and no groups were joined. I only found out by accident that they were under Membership as nothing alerted me to them joining (I was watching the buddypress pages to see if they turned up there - but didn't).
I found by accident they were under Membership.
The Membership plugin needs a MAJOR OVERHAUL in my view and if all the comments listed are read.
I wish Jack all the best in sorting out my site which is experiencing these issues and which I was hoping to have an operational site - but there is too much going wrong.