Have same problem.
I exporting mesh from UE to Blender and back to UE using .FBX fromat.
Losing material sockets.
Also it will much better if socket save material names from any 3D editor app. Now it author applying. And it can cose some mistakes. Exporting from Maya with material name “Lamber1” and after reexporting using UE–>Blender–>UE with new name “mat_01” will add new socket to model in Unreal.