My instinct is that some of the faces are flipped. This causes them to be effectively invisible to some apps.
Previously I would have said to inspect it in Meshmixer, but apparently that’s an old product. I suppose you could use the built-in Fusion tools to inspect the mesh. There should be a way to inspect and flip any inverted faces.
Given that you bought the mesh, I wouldn’t be surprised. It’s amazing to me how bad thw quality of some meshes are online.