There is an issue with using LWHQ hair exported with characters from CC4, where Lumen in darker environments will render hair completely black, which means you can not use the CC4 characters in dimly lit environments. Please, investigate the issue and update Lumen support for the hair shaders, as the paying users of your software are expecting things to work without any custom implementation or spending days trying to find a fix.

Ways to test:
- In a new blank scene, use Post Processing volume with Lumen GI enabled, place a cube in the scene and scale it up to create a shadow area, position a CC4 character outside of the shadow, note how the hair looks, position inside the shadow, note the hair will become completely black.

N.B.: I have tested using other hair shaders made by third party Unreal marketplace sellers in the same conditions, they work fine, it means something in your shader is causing the issue, and it's not Lumen problem.