Try removing the specular. You don’t really need that for UE4. It’s there so it can be used, obviously – but I’m not really sure what purpose it serves. That might be messing with your end result.
Also, when googling for information etc, it’s important to note that UE4 uses a Metal/Roughness PBR workflow. Unity/Cry use Spec/Gloss flows.
I also dug this up for you. You may have already seen it. But it’s a good introduction to materials in UE4 and it explains the basics of UE4’s PBR workflow and what the different texture maps mean in context.