This kind of problem occurs because of a fundamental aspect of parallel projection: the distance of the image plane from the actual object has no effect on the size of the image. In parallel, zoom works by scaling the image, not by moving the camera. So, it is possible to get the camera at a very large distance from the model contents. At that point, strange errors start to occur because the graphics can’t precisely resolve where things in the model are located.
SketchUp was designed as a 3D modeler and intended to work mainly in perspective while modeling. Parallel projection is meant mainly for final presentation in cases where it is mandatory.