1. If the texture passes through Color correction node then it will not be imported into Unreal material
2. Texture emission node assign as normal, Roughness as Specular, Opscity as refraction, Normal as Opacity.
3. Most of the normal map is imported as a non-srgb image.
Currently scripts from users work better than orbx converter in unreal.
Example:
Orbx import

Сonversion of materials using a script viewtopic.php?f=88&t=58420, after imported in fbx format
