I have tested my website with both PageSpeed Insights and Webpagetest and they give a high CLS metric - exactly the same. The problem here is that there is no actual layout shift taking place, especially in viewport area. Or below viewport area. Or way down below the viewport.
According to Page Speed, it is a footer json background animation that counts as CLS (it isn’t). Even worse it gets a very high value: 1.
Such animations as background in some sections are quite usual. Mine is at the footer. The animation script comes from here:
How am I supposed to fix a “layout shift” that isn’t happening?