Users not able to Activate ProSite Upgrades

Hi,

I have a multisite with ProSite enabled. The "Signup on checkout" box has been disabled so that Users can get a Free Blog first, before choosing to upgrade to a ProSite (I did this so Users can sign as Participants without a Blog).

Ever since "unchecking" the "Signup on checkout" box, and letting BuddyPress handle the initial free registration, my Users haven't been able to upgrade to Pro. I find this odd, because previously, when the "Signup on checkout box" was ticked, Prosites worked absolutely beautifully.

So, here are my specific issues when a Free User tries to upgrade to any ProSite Level:

1. After completion of PayPal checkout for a new ProSite (Live Checkout) no ProSite upgrade is processed.
2. The User is redirected to a page "Finalising your site..." (see attachment). Shouldn't this be a "Congratulations on your LEVEL Upgrade" page?
3. Also, the admin login URL in the "Finalising your site..." points to the primary domain, not the multi-site sub-domain that the User owns.
4. No ProSite upgrade confirmation email is sent to the User.
5. When the User tries to upgrade to ProSites again (hitting the ProUpgrade button on Dashboard), they are redirected to the Pricing Table at https://..domain/register/, but a notification at the top of the page reads: "There are pending changes to your account. This message will disappear once these pending changes are completed." Nothing happens.

Very strange situation. If anyone can help, I would greatly appreciate!

This is a continuation of https://premium.wpmudev.org/forums/topic/can-users-register-as-participants-only-with-prosites#post-1201828. I have not been able to resolve for a few days.

Simon