Unsolved Using boolean modifier in Blender causes parts of a mesh to disappear in-game

I'm not sure if this is a bug with BeamNG or if I'm doing something wrong.
Simply cutting a hole in a cube using the boolean modifier causes the inside faces to appear invisible, even though the normals appear correct in Blender. I've tried recalculating the normals, flipping the normals, disabling smooth shading/auto shading but it doesn't do anything. There's also no errors in the console either.
Any way to fix this?

 

Yes, I made sure of that.

 

No I've already done that a few times, same result

 

Yep, all zeroed out

 

Custom material and texture, nothing transparent in the texture nor any transparency properties enabled in the material

Also uvs are properly mapped as well

 

Try selecting the invisible faces and going to mesh -> normals -> flip. Should work
--- Post updated ---
Found an image of the UI on the internet, here is where Mesh is

 

I've done that, still no shot

 

Hmm… Strange.