The codepen is the same as what Jack posted, within the browser (not the codepen viewport) it bounces around to reveal the body below, this is hightened on mobile scrolling horizontally goes to slow and causes the pull whilst vertically is too fast.
It may be to do with the speed or ease? but when you compare the two, the scroll is much smoother on the 'purple' codepen then with the original two versions especially on mobile.