OK, I've got some clarification from MP about how they flag changes in WP user role.
Hopefully this make some sense to you...
MemberPress adds to and removes from the default role(s). So the WordPress hooks would be add_user_role... https://developer.wordpress.or...../add_role/ and remove_user_role... https://developer.wordpress.or.....move_role/
Do let me know what you think and how we can run some tests to debug.
We were looking at this the past weekend. I think we are not properly handling the remove role hook...
Investigating some fixes but will take a few days, possibly until the weekend. Would like to get it in the upcoming 5.8 release if needed