I have a similar / related issue. I’m using Restrict Content Pro’s registration page with the latest Buddypress version (12.1.1) on a staging site and my registration page broke. It told me “Member registration is currently not allowed”, even if I disable the buddypress plugin.
*Update* – I read through the earlier post and found the first workaround – going to Buddypress Settings -> URLs, but did not see any option to change the register slug. I had to briefly turn on wordpress general settings “Anyone can register” so that more options would appear in “URLs”. I was able to set the slug to something else like ‘sign-in’ and that seemed to allow my RCP registration to function again.
Just to check, I disabled “Anyone can register”. Seems like the BP slug change stuck and my RCP registration is operational.