How were you able to get Apple to accept the app when it's locked by a login screen? I suffered with 2 different apps that had been rejected because they required the user to register/login before they can use the app.
you can add a test login username and password in the meta data
It's not about that. They say you cannot require the user to share personal info before using your app. Maybe it's because you are registering with a username and not an email.