When tracking planes vertical position, as you move the camera around, they drift vertically by a few centimeters, in a bobbing motion. This is not apparent in Unity ARKit Plugin, seems to only happen in ARFoundation. Could this be due to auto-focus? Or new points being added? If you spawn a cube using the place on place scene (with a light that casts shadows), and move your device in and out towards the cube, the drift can be seen quite clearly.