hi! do you have a resolution for this issue? It is happening to me too!
I can add a user from my admin WP panel, but cannot register using the /register page: I enter all the data (name, username, etc) click on “Complete Sign Up” – > I’m back to the /register page (all the entered data disappeared)
– I’m using the default theme
– the “allow anyone to register” option IS selected.
– tried it with ALL the plugins disabled