Not sure what’s happening with the ranking algorithm, but it seems like the default main page is still displaying the same set of popular posts from a few days ago.
But if you switch to sorting by “Top Day,” it’ll show fresh popular posts from the past day.
I gather there is a bug in the code for what generates the “Hot” sort and that it only resets when the server is restarted. I believe there is already a fix on GitHub, but person that runs the instance needs to implement it.