Yep, I've noticed it too. Something has changed in the latest upgrade. We'll have poke around and see what we can do. In the mean time, sorting by new or new comments will get updates through to you
I don't think old posts are changing rank anymore. It's like every post pre-update is frozen at the activity score it last had.
That's what I'm thinking happened, my front page looks identical when I sort by hot/active
There is currently a bug in Lemmy that causes hot/active to get stuck, should be fixed in the next version See: https://github.com/LemmyNet/lemmy/issues/3076
That'd have to be finetuned in the lemmy code and rolled out with a new version. Also, those algorithms are insanely complex, companies earn billions over those pieces of code.
Nevertheless, I'm certain someone's already working on it cause open source rocks