Pic 1: It seems your normal of the top plane is reversed. You can ensure your normals are facing the correct direction in Blender for exporting. For a quick check, you can try checking “Two Sided” inside of your material properties which will ignore culling the backfaces. I would fix the reversed normal though as it would be the correct fix.
Pic 2: It seems yo have no UV mapped to the cube.
Good luck!