Any CadLwPolyline with a coordinate of 0,0 ignores that point as valid coordinate. You can use the following example from another post to view the issue. This will render a triangle rather than a rectangle.
using (Cad…...(CadImage cadImage = (CadImage)new DxfImage(CadAcadVersion.AC1032))...polyline = new CadLwPolyline(); polyline.Coordinates = new List();...