Hi Karol,
As a further update, the SapMList-iScroll.js code now only invokes iScroll on mobile devices since the native scrolling is working correctly on desktop. This way we see the native scrollbar on desktop. You can download from this link.
Overall, this workaround seems to resolve the mobile scrolling issue. However, if possible I'd like to determine the reason why native mobile scrolling is suppressed by Design Studio, considering that it works correctly in standalone UI5 applications.
Thanks,
Mustafa.