I suspect the issue has to do with the size of the drawing canvas.
Don’t make it the size of the layout, just make it the size of the screen, and position it to the scroll position.
You could make the draw reactance still cover the layout, or just make it cover the visible view area.
Since it is visual effect you don’t need it to be bigger than the screen. Besides that will save video ram too.
Anyways the reason the size of the canvas is probably causing your issue is the canvas is using a texture and webgl has a maximum texture size per device which is smaller than that layout size.