When checking out the MDN demos on https://developer.mozilla.org/en-US/docs/Web/CSS/scroll-snap-type with `scroll-snap-type: x mandatory` selected, it acts a bit jittery when slowish-ly scrolling over the scroll container and then releasing. Just before it snaps, you can see it jump back a little bit. See recording at https://www.youtube.com/watch?v=vLapfq0flMM You can see it really good at the 4 second, where scrolling back from box 3 to box 2. It jumps a little bit back, before snapping.
What Safari are you seeing this with? STP 139?
Seeing this behavior in both of these versions (on macOS 12.1 (21C52)): - Stable: Version 15.2 (17612.3.6.1.6) - STP: Release 139 (Safari 15.4, WebKit 17613.1.14.41.2)
Updated my machine and Safari TP. Seeing the same behavior on the latest macOS 12.2 (21D49) using STP Release 139 (Safari 15.4, WebKit 17613.1.14.41.3)
<rdar://problem/88584478>