Here is a somewhat strange bug. One area of this trimmed surface does not respond to Contour, Section or Project. The remainder of the surface is okay. See attached file. The red line is perpendicular to the contour planes. I also created a line in the location of the missing contour in the front view, and tried to Project it onto the surface - nothing. Also tried using Section in the same location in the front view - nothing.
However the untrimmed version works properly.
Contour Problem.3dm (109.9 KB)