To me, it seems like this happens when the total number of posts exceeds some threshold... When that threshold is exceeded, as new posts come in, the scroll position is changed. pulling you "up" in the scroll.
One of the thongs that bug me about nostr:nprofile1qqs24yz8xftq8kkdf7q5yzf4v7tn2ek78v0zp2y427mj3sa7f34ggjcpzamhxue69uhhv6t5daezumn0wd68yvfwvdhk6tcppemhxue69uhkummn9ekx7mp0qyg8wumn8ghj7mn0wd68ytnddakj703s8dt a lot, is that the home feed frequently jumps to the top, and you have to sscroll for ages to get to the previous spot.
The number of duplicate content is really large...
Discussion
... Total number of posts *in memory.