Beehaw is defederated with lemmy.world, so those posts won't be updated with the content from beehaw.

Yes, you are right. But it had 3 days to sync. The oldest comment is 3 days old. Here is the same thread visible from another instance, much more up to date. I hadn't noticed that beehaw.org is down though. That could explain it. I still find it odd that this instance would not have a single comment on this thread over these 3 days but... yeah I'll take that explanation for the time being, I'll check again when I notice beehaw is back up.

Do you know how the fediverse works regarding this?:

• If I comment now on that thread on any instance, say, on lemmy.world or on the other I just linked, does it need to first sync to beehaw before it propagates to other instances or would other instances get load my comment even while beehaw is down?

If we take beehaw being currently down as a possible explanation for not seeing any of that thread here then I suppose first the comments need to reach beehaw.

I may as well ask another question, any idea how I would find that thread easily on lemmy.world? I tried pasting the full URL in lemmy.world's search but didn't find it, I had to manually go into that community in lemmy.world's instance and dig through the history to find it. In this case I assumed I would be able to find it by searching the full URL since the thread already is visible in lemmy.world, even if with no comments.