I had this problem before, and here's an answer that worked for me. https://forums.unrealengine.com/development-discussion/rendering/28835-substance-to-ue4-issue-black-metal-in-ue4-viewport
So I'm using a Metal/Rough workflow in painter and in UE. I'm using the environment map "bonaficio aragon stairs" because its at the beach and my scene is at the beach. and lastly I pack my Roughness, Metallic and AO into one map and its definitely hooked up correctly. Yet my metallic looks completely black in UE. Here it…