In UE4.26 path tracing does not work with SSS Shaders , that's why you see green.
In UE4.27 it does work with SSS but you will have some issues with the eyes. ( you have to deactivate eye occlusion )
It is not CC3 related , with the upcoming UE4/5 updates it should work , it is still experimental.
Path Tracing in UE4.27 :
