Weird artifact showing up in .fbx .obj exports

I’m getting a weird artifact (a web) when I export to an .obj, or .fbx file. it doesn’t show up in an .stl file though, and I can’t figure out what to do about it?

here is a link to a folder with the .blend file and some others.

I’m couldn’t even figure out how to google the problem, I’m not familiar enough with the terminology to even ask the right question.

I’m probably going to slice the mesh in half and mirror it and reattach to see if that helps, but would love to know what’s going on.