do Reset XForm. Then convert to editable Mesh and convert back to editable Poly again. This should work! Also check backface culling for if you normals are flipped inside out like m4dcow said.
I think M4DCOW might be onto something, it looks like an internal projection? Are the normals on the low poly inside out? If you apply an edit normals modifier to the low poly are the normals pointing in or out? Flip them if the are facing the wrong way. Next up, are there overlapping UV shells? You should offset all but…