So Apple Developer now requires "account holders" to have two-factor authentication enabled, which is good. But the method they suggest you do is a bit cumbersome and requires you to log out of your existing Apple ID unless you have a separate device. Fortunately, MacRumors had an excellent post suggesting to create a new account on a Mac and set it up on it, so I didn't lose my Apple Pay cards on the phone.
Anyway, when I have done that, I can no longer log in to the account. Once I enter my email address (I don't even get the password), I only get "Error description not available".
Edit: Looks like they've solved it – no one seems to be able to sign in to Apple Developer, and writing something in the email field resulted in that error. Nice one / s