If you have trouble drawing out the longitudinal profile please try these helpful tips.
Answer: Try using a different drawing style or drawing from a different road model. Is it still the same problem?
Check if any of the layers in the drawing is turned off or frozen?
Try running Reset User Settings.
Answer: Is the road model build for the whole stretch you want to draw?
“The terrain line is missing but I still have values for terrain elevation in the bottom half of the frame.”
Answer: Try turning on Simplify terrain cross-sections in the roadmodel settings. Then rebuild the model.
To access this:
You could also try to vary the horizontal and vertical tolerance.