Could be related to or dup of this bug according to wenson_hsieh@apple.com -> https://bugs.webkit.org/show_bug.cgi?id=183157 Steps to reproduce: 1. Go to this url -> http://jsbin.com/susadajiwe/ 2. Try scrolling colored block, which is iframe with src -> https://whsieh.github.io/examples/scroll-snap-mainframe 3. Notice no snap behavior for the endpoint when in iframe, though behavior works when navigating to it independently.
This fails for me in Safari, but works in Safari Technology Preview 120, so I think this has been fixed by another change.