My first guess would be that it IS the vertex normals getting messed up by Modo. It's one of the few things that I dislike about Modo is that it handles smoothing groups very poorly. Are you using obj to move your models back and forth between Max and Modo? And if so, when you import your model into Modo are you deleting…
Possibly from the obj import settings or maybe the way it was exported? I'm not sure if those are inside out, some look to be gradients? If you click the object, then right click and turn on back face culling do they disappear? If that's the case then you need to flip them either in edit poly > poly mode > select and flip.…