Is this from Blender? Blender by default shows both sides of a face, while most game engines hide the back face. So I'd guess that missing face might have its face orientation flipped compared to the others, and gets culled because of it.
Is this from Blender? Blender by default shows both sides of a face, while most game engines hide the back face. So I'd guess that missing face might have its face orientation flipped compared to the others, and gets culled because of it.