Neither of my posts from yesterday and today have made it out to their communities' home instance (lemmy.world), and neither has received any comments or votes. It seems like something to do with outgoing federation is stuck.
Edit to clarify:
The problem I'm seeing affects posts. I don't know if it affects comments.
It's possible that it only affects lemmy.world communities, but it definitely affects them even on other instances. Neither of these posts are showing up on any remote instance that I've seen:
https://lemmy.sdf.org/post/21620419
https://lemmy.sdf.org/post/21673588
6 days later, it's happening again:
https://lemmy.sdf.org/post/21974478
Completely off-topic:
I'm surprised to learn from the comments here that people on other instances subscribe to this sdf-specific community. I have no idea why they would, but it somehow makes me happy.