Aha! I switched to the Twenty Fourteen theme to see if there could be a theme conflict and it revealed a required registration field that was hidden with CSS. So registration is indeed working.
I had hidden the primary field in the Profile Details on the User Profile page because I didn’t want it editable once they had registered. I didn’t realize that it also hid the field on the Register page, and it is a required field.
Total derp move, but I figured it out. Upgraded to 2.2.0, added my custom functions back in, all good. Thanks for your help 🙂
deleted and recreated the Register and Activate pages
and it’s still not working. Is there something in the database I need to delete to get a clean install of a Buddypress that has a functioning registration?
