Not sure why, but the number of videos shown in the playlist info panel is no longer accurate (at least not for one of my playlists that caused me to notice this problem). I used to use that number of videos as the indicator to stop auto-scrolling. (Which was a stupid way to do it anyways) Due to this miss-match, the auto-scrolling would never stop.
This is now fixed. Now checking for the "ytd-continuation-item-renderer" instead, which seems to get removed from the DOM when there is no more scrolling to be done.