Vertical scrolling hides elements

https://dustarrest.webflow.io/product/15ltr-hydro-filtered-230v-vacuum-maxvac-dura-dv15-hv

I have a sticky element that shows at top and bottom of the screen when scrolling.

strangely on mobile the top one hides by roughly 20px when scrolling down and the bottom one vice versa when scrolling up.

can someone help and explain why this happening?

@webdev @PixelGeek

cheers!
Arran