Sometimes it can happen the faces looks into the inside of the Mesh/Model.
That is reason for unvisible faces Ingame. 
I don't know, which 3D Software do you have (I use Blender), but you should turn around the wrong faces Outside in Editmode.
Hope that help.
Best regards
CDRMVStatistics: Posted by CDRMV — 26 Jun 2017, 17:26
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