It’s confirmed as a bug and can currently be fixed by modifying the shader code here
https://github.com/EpicGames/UnrealEngine/commit/90ef97eee45bdb2665fafbd49d3784241ddba202
It requires recompiling shaders. UDN has mentioned a target fix for 5.5 and probably not a 5.4 hotfix due to it impacting shader cache ddc unfortunately