unfortunately… I am using a Character Creation tool. Fuse. Others have been fine from what I have seen. 
But I just looked at the wireframe and it does look clear to me that there is missing Polygons. 
but when I run the game as the character it flickers between fully textured and the one that is currently with gaps. which makes no sense… I dunno lol. going to try importing a fresh Model and see what happens!