Personally, I needed to redo several times the registration before to succeed, but I do not remember exactly the issue (certainly with the password)
My colleague ZHU reported to me the following issue. If you want to have more details, please contact him directly.
“As a first step I tried to register with my old Username and password. Refused, telling that these were existing. Then tried to change the Username, refused saying the e-mail address is occupied. Then selected an other e-mail in our household. The password however did not arrive. That was the point I contacted Michael. He passed the problem to Daniel who solved the issue. Still I use the km long password with permanent login. After I received 3 messages from WordPress. Do not want to run a risk again”