@paoloemilioserra it seems that FeatureLine.PolyCurve does not work correctly when there are arc segments. It returns a polycurve when all of the elevation points are equal, but it returns null when the elevations are different. The log file says that "points are likely coincident".
paoloemilioserra
commented
3 years ago 
v1.1.14
@paoloemilioserra it seems that FeatureLine.PolyCurve does not work correctly when there are arc segments. It returns a polycurve when all of the elevation points are equal, but it returns null when the elevations are different. The log file says that "points are likely coincident".
Autodesk_Civil3DToolkit.txt FeatureLine.PolyCurve.zip