Scrolling causes images to 'glitch' when I have more than 10 pages piled. (On Chrome, Mac)

Hi. [My portfolio page](https://inkling.ie/portfolio.html) with pagepiling recently stopped working. It's now really glitchy (see video attached). It was working fine before, which makes me think it's to do with Chrome's last update. (There's no issue in Safari). I also tested it with the Lewis themeforest template by inspecting the code on [this page](http://paul-themes.com/html/lewis/demo/work-parallax.html). When I add more than 10 pages to the pile, it starts glitching, just like my portfolio page does.

https://user-images.githubusercontent.com/93086139/138598469-2d0536a3-a868-4d6a-b0f0-cb18fc58f41f.mov

Is there a way to stop it glitching for more than 10 pages?

Many thanks