Edit: Definitely not relevant, it was a problem with the link I clicked
original
Not sure if it's related but I've noticed a couple of smaller communities from other instances which aren't accessible from programming.dev any more, Imaginary Witches and Imaginary Fairies. They give the very helpful error "unknown", this might be a fun one to try to track down. They're accessible on the source sites (1, 2) and other communities from those instances seem to work.