You open Google Search Console, and it is full of green arrows. Position 4 turned into position 2. Position 2 turned into position 1. You did the work, the work paid off, and then your traffic graph started pointing at the FLOOR.
I have watched this happen to sites with clean rankings, fresh content, and zero penalties. It is one of the most confusing things in SEO right now, and most of the noise about it just repeats the same reasons.