Unable to create new account after deleting one with same email

[MonoScyron]

Registered an account under an email address, then deleted it to change the username. Attempting to register a new account with the same email and different username sent a verification link that resulted in a "Register failed" message. Attempting to sign-in using GitHub results in this page being displayed:

Clicking the sign-in button directs to the same page.

Additional context:

• The first account was created with a different username, but all accounts afterward have the same username
• All accounts were created with the same email