Hi Rob,
This is a know bug that we have on our list at
https://mcneel.myjetbrains.com/youtrack/issue/RH-66088/Curve-is-gappy-in-V8
Curve drawing got a lot more complicated in Rhino 8 and appears to be failing on some nVidia drivers. I typically do all of my graphics development on Intel since traditionally if I could get things to work there they worked just fine on nVidia and AMD. I’m getting an nVidia based development machine set up to try and track this one down.