Hi
Then some of the contours might got lost at your two import stages.
They get lost with the InRoads Surface import. See the triangles (white) I have created after importing the XFM-Features(line strings) form your dgn.
Something must be different with some of that XFM-Features, that InRoads does not import them.
They are XFM-Cells, they will not get imported by InRoads. You have to find a way to "explode" them.
You should contact the Bentley support !
And for a good surface for further work it is not the best idea to import contours. You will have differences anyway.