There is definitely a technical issue with federation, lots of big database changes that should help with site stability and federation are coming in the next lemmy versions.
The other issue is how sites with downtime are handled, because if sites go down it can break federation.
Lemmy.world's uptime is rubbish at the moment and this is causing them not to federate properly with all instances, it's a gamble. You can see a post on lemmy.world in relation to some of their downtime today, which was about the same time that post was created, and it's possible that we just got unlucky with the federation activity not reaching us.
There isn't currently a way to force a refederation that I'm aware of unfortunately.
This takes me onto my "stop using lemmy.world" rant but thats not entirely on topic here, but suffice to say people should really stop using lemmy.world and spread out around the fediverse.
Hopefully that answers the question but let me know if not :)