I was unlucky enough to have to regenerate racket2nix catalog.rktd right after #MSFTGothub and one developer moved over to gitlab.com and hasn't had time to update pkgs.racket-lang.org yet.

Adding some manual exceptions to look in the new location. Luckily it was easy to find, with retained user name and repo names. And I think it's just that one person (so far).