There was a large backlog of emails due to notifications being broken and offline for several days.

It should be catching up now.

Can you confirm that those folks have gotten their emails now?

I confirm. Thanks.
Now there is another problem.
"I finally received the email, but the token is no longer valid. I can't re-register because seemingly every username is taken. Any idea where I can file a ticket about this?"
How could he proceed?

They can go to:

https://accounts.fedoraproject.org/register/confirm?username=

and tell it to resend the email (filling in the account name they used for )

Or we can clear the account and they can start completely over on it.

We are setting up a script that will remove these 'partially' registered accounts after 1 week moving forward, so once thats implemented they could also just wait a week. :)

Hi there, I am the user in question. I followed the instructions above and everything is set up now. Thank you!

Glad to hear it!