Yes, there isn't any such validation. If you have required registration ticked and requires email verification to activate account than add a js to hide the registration field and populate it when email address is entered
thanks for your guidance, here is the PHP error and it led me to the solution:
Fatal error: Uncaught Error: Call to undefined function bccomp() in
this prompted me to install bcmath:
sudo apt-get update -y
sudo apt-get install -y php7.2-bcmath
restarted apache and the ...