Is there any update on this? I'm experiencing a very similar problem with a grid of PKCanvasViews only since iPadOS 15. My canvases' presentations stay blank although the touchesBegan/Moved/Ended/Cancelled events are registered. The strokes are just not visible. No unexpected background coloration or faulty black rectangular presentation of strokes here. (I set the canvases' background color to clear.) Any first and second grid PKCanvasView I draw in will behave normally. Any third grid PKCanvasView I draw in will show the stroke while drawing. When finished, the stroke will disappear and several insufficient memory errors are thrown. Any fourth or later grid PKCanvasView I draw in will show neither currently drawn nor finished strokes. Throughout the drawing, insufficient memory errors and occasional non-zero time already exists errors are thrown.

[Moved comment to an answer below]