It might not just be lemmy.world, but several times recently I’ve made posts (usually to !helldivers2.lemmy.ca) that I check throughout the day. Then like 8 hours after I’ve made the post, I’ll see comments appear from people on lemmy.world that are several hours old.
It seems like there can be a queue that gets build up and then is suddenly flushed.
I see it happening the other way as well. This morning I made a post from my sh.itjust.works account and then switched over to a lemmy.world account and can’t see it. So the delay is going both ways.
Some of the instance admins have been poking at this lagging federation issue for a few weeks now, trying to figure it out.
The Reddthat admin noticed that Lemmy’s federation process can’t seem to meet demand in some cases. Reddthat has had trouble staying current with lemmy.world due to the network latency between Europe and Australia: https://sh.itjust.works/comment/9807807. I understand that lemmy.nz has seen this, too.
Another thing that has been noticed is spamming of actions from kbin instances. It looks like some process gets stuck in a loop on the kbin side. https://lemmy.world/comment/8961882
I’m sure there are other contributing problems that still aren’t well understood. This software is a work in progress, after all.
These posts are enlightening, I think reddthat is right lemmy will need to using batch messages on longer intervals soon, that’s pretty unsustainable in current form. What an interesting scaling issue to encounter.