Ask HN: Erratic HN front page algorithm

Last week I had two submissions reach the HN front page. Before that, I assumed the ranking followed a roughly monotonic time-decay curve once a post peaked. While watching these two posts, I noticed something different: their rank would sometimes improve after declining, and occasionally oscillate back and forth (Here is a graph showing this behavior: https://imgur.com/a/AQnSh6I). what mechanisms in the HN ranking algorithm cause this kind of non-monotonic movement. Is it due to vote weighting, comment activity, re-ranking batches, or something else?

The graph is from: https://track-hacker-news.com/

EDIT: This is the post referenced: https://news.ycombinator.com/item?id=46512881