Please see attached file. I have created a section at 0+150 on my corridor. You can see the assembly in the drawing (I copied it over from another drawing). If you zoom in on the section you can see a magenta line (top of corridor) and an orange line (datum of corridor). Also, if you look at the Sample Line Group Properties dialogue box you will see that only the OG and the corridor is to be added to the sections. Further, in Toolspace, under surfaces, there is only one surface, OG (original ground). So, how can the top and datum linework be added to the section when there isn't even a top or datum surface? Even if there was, they are not in the Sample Line Group Properties dialogue box to be added to the sections??
Found a solution. I went into Sample Line Group Properties, sample more sources, removed the sampled sources (OG and the corridor), ok/apply to open dialogue boxes. I then reopened Sample Line Group Properties and added OG and my corridor back in and my issue was solved!