hi dale. seems this issue happen again.
and I found some computers will not have this issue others will.
after many works on this issue, I found if I change the Rhino render background color setting to “Solid color” mode, this issue will disappeared, but if i use “Environment” mode, this issue will happen. you can see the issue link here: How to set background to solid color mode use RhinoScript. would you kindly help me on this? thank you very much.