I have it happen a lot when I'm doom scrolling, pretty far down, and open a post (but I don't know if opening a post triggers it or I just notice it more).

I then go back, scroll a bit more, and find the same post I just saw and the ones around it too.

I use the all - top 12 hours filter when it happens.

I've seen it as well. A part of it is because posts get down voted, so when you scroll down it gets displayed twice since it moved in the ranking in between loading. This also means if a post gets up voted, you can easily miss it. It's only an issue with posts that have few votes usually, so not a huge deal.

But I've also seen where the same few posts just repeat twice for seemingly no reason. I'm not really sure how the data gets retrieved. With other systems I've seen a "session" associated with a cursor. That cursor moves through the data, maintaining the order. That way it doesn't matter that stuff changes in between client data retrieval. Lemmy doesn't seem to work like that, simply querying the database with filters. That isn't the best honestly.

You sure they're not cross posts?

It's been fixed a while ago, just not released yet. There is few blockers.

Been noticing the same thing, but I use All for my feed.

Yeah, ive been seeing it off and on for months. On "top 12 hours", not sure about others.

I notice they sometimes have different vote and comment counts, implying they loaded at different times.

I'm assuming it has something to do with the way results are paged, and being loaded a page at a time as we scroll.