Kind of falls under the 'Too Afraid to Ask' category, I guess, but I've been curious about this for a while. Did something actually happen at some point, or was this just a procedural thing that wasn't ever followed up on?
It's mildly annoying given how large they are.
Edit: It's possible that this isn't a federation problem at all (as discussion is bringing to light) but something else entirely. Regardless, though, something is going on.
It's also possible that the site I link below is out of date, so maybe don't take that as gospel. I bookmarked it a year ago and just hit it up to check on this a few minutes before posting, so I haven't been keeping up with it.
Doing a little more digging in light of the above, it's possible this is related to this issue, and there's just an extremely long delay before we get content from lemmy.world. Weirdly, though, it doesn't seem to be the case with other instances - maybe because of their size? Either way, looking at the same posts on our instance and 3 or 4 others, we seem to be the only ones not getting the replies. So something's fucked, maybe.
If you're on lemmy.world and happen to see this, drop a reply in here, maybe - I'd be curious to see how long it takes for us to see it (or if we can at all).
I see plenty on my feed from .world, and checking my profile, I've gotten replies from .world users as of at least two weeks ago, which implies that they can see posts made by accounts hosted here (else how would someone there see my comment to reply to it), unless something happened relatively recently.
I'm assuming this is related to the performance issues that've been being posted about on Telegram over the past hour. Digging deeper, I'm seeing their replies, too, but they're massively delayed. (The .world reply on this thread still isn't visible, for instance.) Will see if the situation improves when the server issue is sorted.