Hi Leonard, that looks like a polygon modeling issue - if you're going to grab just a single vertex and pull it around you may want to export as all triangles rather than as n-gons. Or C4D also probably has a triangulation command that you could apply to it inside of C4D.

N-gons made up of many points do not behave very well if they get some points warped so that the n-gon is not anywhere close to planar anymore. It makes the triangulation of the n-gon to become ambiguous.

Check out this polygon modeling video tutorial for an illustration:
http://guerrillacg.org/home/3d-polygon-modeling/multi-sided-polygons


So that's probably the main thing you're running into.

You may also want to generate an even denser mesh than what you show there.

- Michael