I followed this tutorial to make a POM material for my brick floor: How to Do simple Parallax Occlusion Mapping in unreal Egnine 4 - YouTube
Instead of feeding all that setup for UVs on POM node, I simply fed texcoord  into UVs input on POM node (I don’t know if it has anything to do with the issue).
After applying material to the floor mesh, it worked fine. However, if I rotate floor mesh 90 deg. to make it a wall mesh, POM material turns flat black.
What am I missing ? How do I make sure POM material works for floors/walls/ceiling ?
P.S. I am using UE 4.22.3