The above screenshot shows raster compilation (photoreal). Traffic is vector (shp2vec). Also the above are not errors, they are warnings and will be ignored by resample. Are you selecting the lines before trying to compile them?
I don't recall any width minimums for display / non-display of CVX vector roads with freeway traffic such as applies with BGLComp XML-based RWYs, Taxiways, etc., but it is an interesting and valid question.
Perhaps you might attach or link to an example FSX SDK-compiled example of CVX vector roads with freeway traffic for the area in question, so that those of us who do not yet have P3Dv4.x may test it and help with further determining whether there may be a difference in the behavior of CVX vector roads with freeway traffic in the P3Dv4.x SDK SHP2VEC BGL format ...compared to the FSX SP2 SDK SHP2VEC BGL format ?
I attempted viewing the 56 Byte CVX_PROJECT.BGL file attached above with both the FSX SP2 and P3D Version 188.8.131.5286 SDK TMFViewer, and I tried decompiling it with Patrick Germain's CVXExtractor GUI; both were unable to process that file.
What FSX or P3D SDK version was it compiled with ?