Toon shading: Why my black outline covers full of the surface?

Unity Engine
1

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I use the internal Toon Shading: Basic Outline.

It’s normal in Prefab’s Preview (Inspector). But when it’s instantiated or dragged in the scene, some parts of the model become totally black (the outline covers all the surface of the model).

Why does it happen? Is there any approach to fix this?

LEFT: in the scene, NOT correct
RIGHT: in preview, correct

2

Is it because of the lighting in your scene? Not too sure since i don’t use the toon shading. Yet.