I have been exploring the quirks of scrolling my gallery under improved rendering.
On the desktop in Chrome: Using the scroll wheel on my mouse, each 'click' (rotation) of the scroll wheel moves the gallery view by a slight amount, as expected. However every second or third turn of the scroll wheel seems to cause the gallery to bring in more data, making its total height longer, and causing the scrollbar on the right to seemingly refactor where it should be - again all as expected, except the very next scroll seems to be wildly unpredictable - jumping several rows.
This is all magnified when, in normal use, you deliberately scroll down multiple lines. The overall scroll is jumpy and feels disjointed from the number of times I've turned the scroll wheel. Then when you see the item you want and stop scrolling, the view invariably does one last jump in another direction before you have chance to click.
On the mobile app, Android: Scrolling only ever works less than the total height of the screen before it hangs for up to a second (in other words you touch and drag to scroll but you can't smoothly scroll even one page worth). You usually have to let go, and touch and scroll again to get futher down the gallery.
It strikes me that the issues are in some way related to whatever goes on when PowerApps dynamically loads data as you scroll. This issue doesn't exist in Classic Rendering.
One more quirk that I think is related: if you turn on the navigation buttons and set it to scroll just 1 item at a time, again it starts jumping after 2 or 3 successful scrolls - suddenly it jumps 2, and it continues in this manner, alternating between single and double item scrolling.
Dave, we're tracking this issue as #90716266. Can you confirm that indeed toggling off improved app rendering resolves the issue?
Clarification: as you're scrolling through the app, are you clicking any controls in the gallery or interacting with it in any other way besides scrolling?