I cannot understand where the problem comes from.
I’ve imported this model as a FBX file generated from 3DS max and I apply A mobile/Bump Specular metarial on it. So far, the normal map has a uniform color.
Waiting for your help.
In your model import settings you can try to have unity calculate the normals. If this doesnt work you need to edit the 3ds max file and check the normals. If that face has an inverted normal it is a modelling problem and you need to fix it outside of unity.