Ordinarily, the scroll on background scroll works fine. However, when the background is solid black, the scrolling object glitches when it approaches the edge of the screen.
To reproduce: create a simple object (shape, etc), set the animation to react on bg scroll.
If the background is black (#FF000000), the object glitches. If the background color is anything else, including #FF000001, it works fine.
I'm using Nova Launcher on a Pixel 3