I don't know how to answer that. I believe it has something to do with normals. It's not the green channel needing flipped if that's what you mean. It looks fine in 3ds Max and Marmoset, but not UE4. I have confirmation that it shows the error in another engine. I threw it into a UE4 marketplace scene. It's fine until I…
I've never worked in UE4, but in the UDK, I've seen a simillar issue, my solution was to have UV shells in their own smoothing group, or in maya: harden all shell border edges, then re-bake.
It's an issue with the binormal not being flipped when the UVs are. Fairly common issue with game engines. You can either try to fix it in the shader (I think UE4 does the transforms in the pixel shader anyway) or possibly in the mesh... although I suspect that would need some coding.
:poly102: You truly did. Wow. Thank you. In UDK I was checking the normal compression on import, now in UE4 I'm not getting that import option screen but occasionally seeing the message on the bottom-right of the screen telling me something imported as a normal map. The detail maps were all fine but several of the baked…