I've been noticing that when I open a page for a post, the upvote counter seemed to bounce around wildly. Figured it was just something to do with the enormous load on the instance(s). However, I just noticed something extra strange and thought the info may help someone troubleshoot and fix it.
I saw a post come in for the lemmy.world community that just got posted less than a minute earlier. I opened it, and saw the upvote counter was something like 745, which seemed odd. Then about 10 seconds later while I was watching, it changed to 128. 10ish more seconds go by, and it changed to 996 (actual numbers were slightly different as I wasn't trying to memorize them).
It seems highly unlikely that a post less than a minute old would have any of those upvotes. I suspect that there's an issue where post upvote counters are getting updates with the counters from other posts. When you hover over it, the popup seems to reflect a more accurate number.
Not sure if this is a lemmy.world issue, or a lemmy as a whole issue.
Lemmy uses a websocket connection to send updates to your browser. What seems to happen is that when you go from the thread view to a post, the websocket still receives updates for all posts, and the upvote counter changes whenever it receives an update for an unrelated post.