Hi there, It may be your normals. In blender try shift N to recaluclate the normals. Im not 100% sure what the problem is becuse i would have to see it for myself. One thing you can do is use back face culling. This will show the faces of your model and what they will look like in game.
off:
on:
Another thing you can use is face orientation. This will show the faces. Blue means your nomals are ok, red means you normals are wrong.
It looks like this:
One last thing check you modifers are ok and are applying.