(Triangulation?) artifacts in marmoset

refraction

I'm trying to bring this low poly mesh into marmoset and can't get rid of this giant spike of geo flying off into space. I've tried changing the topology at the root of the spike, tried softening normals and making sure the UVs were okay.. what generally causes this?

Thank you!

refraction

FYI, re-tweaking and re-exporting from 3dcoat got rid of it. *shrug*