I've finished my binary glTF exporter so that it is compliant with the requirements for Paint 3D.
At the present time, Microsoft is not compliant with the glTF specification. (They are working on it).
Further more, it is immediately apparent that Paint 3D will not be suitable for painting exported SketchUp models...
Model in Sketchup:
Model in glTF viewer (WebGL)
Model in Paint3D:
I don't understand the internals of Paint 3D enough to understand why it displays the pixelation causing the zombie-effect.