Why it matters
Long Animation Frames (LoAF) during scroll show script that delays rendering; the attributed script is the culprit.
How to fix it
Move the attributed work out of the scroll path: debounce with requestAnimationFrame, precompute, or yield with scheduler.yield().
References
More smoothness rules
void smooth reports 13 rules in this category. How the page feels after it loads: dropped frames during a scripted scroll, long animation frames, INP of real clicks, shifts after input, animated layout properties, idle rAF loops and reduced-motion handling.
scroll-jankFrames are dropped while scrollingscroll-listener-nonpassiveNon-passive wheel/touch listenerinp-slowInteractions are slow to respond (INP)layout-shift-after-inputLayout shifts long after an interactionlayout-shift-on-scrollLayout shifts while scrollinganimate-layout-propertyAnimation of a layout-triggering propertytransition-alltransition: allwill-change-overusewill-change is applied too broadly