Federation Bugs are still around, and this is no exception.
Try going to the "search" button, and copy/paste the comment's URL into the search bar. This will force the lemm.ee server (literally the software) to try to fetch that comment specifically. From then on, the comment should be "known" by the system and stay up-to-date from there on.
Then again, it shouldn't have desync'd in the first place. So there's clearly some kind of obscure desync/federation bug happening.
Thanks. I pasted the link in the search bar. Does it take a while for things to sync? I don't see anything a few minutes after doing that.
I don't have a lemm.ee account... but I'll try to see things from your perspective.
I went to : https://lemm.ee/post/5191261?scrollToComments=true
Looks like all the comments are there? Is this the thread you were trying to look at?
That's the thread. When I use that link while logged into lemm.ee I don't see any comments. But I can see comments from here while logged into my lemdro.id account: https://lemdro.id/post/820611
You can make a post here if you're looking for support with any issues!
For general discussion about lemm.ee, please post in !meta instead.