Have you tried turning on the triangles or moving into 3d view, or object viewer. The problem maybe that it's adding vertices to a feature line where it crosses an alignment or other feature line making the surface go up and down from z=0
R10 - 2020 ACAD
2008 - 2020 Civil 3D
2014 - 2020 Plant 3D
2014 - 2020 Revit
V8i - V8i SS4 Microstation
Infraworks
2018-2020 Inventor
2020 Navisworks