Huh? So after getting Rhino 6.4 running on my machine I have several weird happenings. The clipping of objects with GPU Tessellation checked still happens. Switching it off cures the problem. I guess this must be an AMD problem.
I imported a Background image bitmap into a layer. However, switching off the does not hide the bitmap. Maybe I’m doing something wrong.
When I select any create tool, curve, solid, etc., these odd lines appear. (see pic) RH 6.2 worked fine for me.