When creating a cross-section, the surface line is not displayed.
If the surface in question has no breaklines, only random points, one possible solution is that on the Advanced tab of the Surface Properties dialog, the "Use Features Only" option is toggled on. This option alters the display characteristics of surfaces in cross sections so that the surface data line is displayed between points extracted only from breakline features in the surface. Since there are no breaklines in the surface, no surface data is displayed.