The Dynamic Registration & Auto Member features should be working fine again now
I'm afraid the members affected will have to re-register though.
I've just checked your board, and Dynamic Registration is enabled on your board, you can disable Dynamic Registration on your board by unticking the box next to where it says 'Use Dynamic Registration?' in the General Board Settings section in your boards Edit Board Settings screen in your Admin Center. That will take potential new members to the default BbBoard registration screen to register instead of your boards own registration screen