Hi, I can tray to give you a solution, as I had the same issue.
Did you made your object with Blender?
In this case , you need to go to the material shaders in Blender ad see if there is a normal Map attached to your material that in the smartphone shows black.
Delete the normal map and export again your scene.
This method works only if you used Blendner
Hope it will work,
FB
