@pitaj Yes it does sound like the same issue, I did notice that even after I deleted all the users, if I tried to register a new user with a new email that I know was not present previously the new user ID is sequential so that tells me that even though I deleted all the users, there is still some data existing somewhere in the database that was preventing registrations using any previously known email.
As I said, I just gave up and deleted the database and started fresh, took me much longer to reconfigure everything, but was the only option I had since I couldn't get any user registrations to work.