The real answer to this is to uncheck sRGB in the texture properties. It seems to use a bootlegged world normal, otherwise. It is also best to have the Compression Settings = NormalMap (if it is not).
Mirroring UVs should always be supported by engines, as they are great for optimizing texel density and not having to do re-work. Especially useful in Environment Art pipelines.
- Note: Importing a fresh normal map to the project, and relying on UE’s auto-compression algo, automatically sets these properly.
