I think that is sometimes caused by using an onscroll event without the {passive: true} option set. Even better, remove all onscroll events (including from libraries or adverts you may use).

I’m not the previous poster and I’m not sure if this is the same, but on iOS Safari there is something odd about the page scroll. Normally on iOS, when you scroll a page, the title/address bar shrinks. You can tap it and it expands, and tap it again and it scrolls you back to the top of the page. None of that happens on your page. I don’t really notice that the scrolling itself is off, but I’m probably not that sensitive to that kind of thing. This is latest iPhone OS and iPad OS, 13.4.

I know Firefox for iOS uses WebKit so not sure how useful the information is, but the same “issue” is present there. The scrolling is just different.

iOS 12.4. When I scroll up or down normally the intensity of the flick causes it to scroll faster or slower. It feels like there’s a “hard stop” on the page, the scrolling stops sooner. Scrolling slowly seems to be off by a pixel or something, almost like a judder. I didn’t see the same issue on Chrome on my Mac.