I see the problem in the fact that you did not provide the original data of the scene. Therefore, it is impossible to write a shader that will satisfy you. When you used the auto shader, it used scene data, light position, material, vertex data. At the moment, you specify this arbitrarily, which prevents you from getting the same results as an auto shader. For example, the direction of the light source should be indicated relative to the camera position. And not in world coordinates and so on, in fact there are a lot of factors.
It’s strange that your scene disappeared after applying my shader. However, which exporter do you use?