We had a user (school admin) who had initially signed in with 2-step verification and after a long while tried to sign in again. They received the error message "The email address that your social networking service returned is already in use. Sign in with that existing account or change your email address with the social networking service" and did not know what to do.
The platform manager tried to disconnect and reconnect the user to no avail, the error persists. A platform manager should have the option to completely reset a user's access to allow them to choose their mode of login from scratch once more when "weird things" happen.