The question Hello World. Can you see this question? got some close votes very early on, but an hour later it still hasn't appeared in the close review queue. Normally, this happens about fifteen minutes after the first close vote.
Apologies for the inconvenience, and thanks for your patience, y'all. This was a fun one.
The Close Votes queue and some of the others are refreshed on a schedule. The Scheduler service is configured to discover new sites when they join the network (and, in general, new scheduled routes when they're added to the code). This works perfectly unless you somehow end up with the Scheduler deployed with dev tier config instead of production. You'd think that everything else would fail catastrophically in that situation, but no - because the config is also cached. :P
So the Scheduler was happily running and updating for all sites that it was aware of, but didn't pick up either Proof Assistants or Substrate. The immediate configuration issue has been resolved. I'll be following up with folks internally to figure out how we even ended up in this situation and how to prevent it going forward.