This shader have tweak to GGX method change to mobile GGX from UE4 mobile PBR.
UE4.20 mobile PBR updated Blinn-Phong Approximation to Mobile GGX. So, UE4.19 mobile shader change to Legacy.
Update shaders for Substnace Painter 2018.2
https://share.allegorithmic.com/libraries/3341
Phong Approximate (legacy) vs GGX Mobile (UE4.20 after)
https://j1jeong.wordpress.com/2018/07/19/substance-shader-for-ue4-mobile/