"Neutral" Normal Map changes with UV direction

[Secrop]

@Cygon

So the UVs run in different X directions. It shouldn’t matter (and in UE4, Unity 5, Godot 3.1 it doesn’t), but Blender Cycles produces this very visible lighting/gloss difference.

Well, Cycles shouldn’t produce this result unless something in your material deliberately tells the render to do it…
Please post a screenshot of your material nodes (or a blend file with textures packed).