I'm pretty sure this is only visible on c/196 right now because it's grown to the point where there's a new post every 5-15 minutes.
Hours apart, I'll log on and see the same content on Activate/Hot ranking. I'm still seeing stuff from 24-48 hours ago in the first page, which is wildly different behavior than a comparable subreddit where you'd barely see the last 12 hours on the first few pages.
Can this be fine-tuned per instance or per community?
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