Hi @Arkan_Afif,
In the beginning of my work with Shapespark, I also noticed this problem. It disappears when the whole scene increase. Then you also need to increase the light and speed of the camera, but you must reduce the resolution of the shadow in this case.
Increase 5x will give precision below 1 mm.
However, I believe that you will avoid high poly models in practice as your scene will be too large to load and slow to display.
Quantization of the vertex position is a great solution from Shapespark with the aim of optimizing the scene. If you have a scene with over 3,000,000 vertexes, 9,000,000 characters are reduced by quantization!