I can't get Membership to recognize a Paypal payment and activate the user in the multisite load, it does in the non-multisite load we have running. Non-multisite works fine, only in live mode though not sandbox (that's another issue for another time). User can signup, pay, instantly access, and it shows in admin properly as well. However, our Multisite load will only register the user and redirect to payment, but will not assign it the subscription or activate the user after payment is made.
I've tried both live and sandbox, no difference. I noticed that after payment, looking at the url (after it redirects back to my site) says "Completed", has the amount, item number, among several other encrypted things. Seems like it's trying to tell Membership something but it's not getting through.
I copied it to a text file and attached it here, hope it helps.
Using WP 3.12 and Membership 2.03