The section is cutting through everything in the model. By the looks of the section you have cut a section along the refernce line (Mstring) through the gound and stored it in the design model, this would account for the 'Z' where it drops down the to the ground. If you use the dynamic setion tool you can add or tooltip string lables for strings cut to help identify the offending string and then mask it out, or delete it from the model.
Regards
Ian