I am having issuse with the Rendered Display Mode, Nurbs look like Polygons.
I think its happled after my last update two days ago.
Upload an example .3dm file. Drag the file to where you type posts, or click on the vertical arrow icon above where you type posts.
Here is an example:
SAS-Rail_test.3dm (5.1 MB)
I found the solution, its related to the Flat Shading option.