I have a strange issue with normal maps created in Substance designer or xNormal. Where there is a gradual change in value sudden lines appear (as if the color space was compressed). I can not figure out what is the cause. Here is a screenshot (basic material with environment map).
Could you add images of the wireframe mesh you are applying it to and the normal map itself?
The mesh is just a simple plane (2 triangles, both vertices welded.) thie normal map was created in substance designer but this is just a simple perlin noise converted to normal inside SD and exported as png. no baking or any other complex operations 
Would love to take a look at this, Please submit this plane and texture in Unity > Help > Report a bug - and drop the number here
Cheers
Olly - Unity Support
