untangling login/registration issues for my membership site

Hello,

Brand new to WPMU Dev and turning to you because I can’t get a holistic view of my multi-site WP membership site’s current issues from any of my current support paths (MemberPress support team and my own web host tech help). My setup is:

-WP multi-site (one main website and one sub-site) as paid, private, membership blog. It was just the one blog, protected by s2member for almost five years. Since adding the sub-site, registrations weren’t automated as they should be.

-Decided to switch to MemberPress for many reasons and went through the complicated steps of transitioning just after Christmas. Since then, have been troubleshooting login/registration problems.

-MP (MemberPress) doesn’t support multi-site (no membership plugin can, from my extensive research), but it should work on the main site, which it isn’t…correctly. I am concerned that there is some combination of BuddyPress (long used on my main site, mostly for profiles and activity stream) or other plugins causing difficulty, but can’t get a clear response from MP support.

-Test registrations went fine for me and for MP support. 2 out of 3 current members attempting to update their memberships run into error messages, tho’ 1 had success and no issues at all (tho’ her new membership didn’t attach to her old as it was supposed to. I’ve stopped asking members to try for the moment.

Hoping for help outside of MP…that someone might be able to see the whole picture of my setup and help me figure out what needs to be adjusted.