The fix also applies to the latest 4.26 version.
**Shadow.HairTransmittance **parameter. Replace, the constant “1” value by “GBuffer.CustomData.z”
I don’t recommend adding the “bEvalMultiScatter” from the thread. It stopped my editor from loading
-TLDR-
Change this line in Engine\Shaders\Private\ShadingModels.ush:
const float3 BsdfValue = HairShading(GBuffer, L, V, N, Shadow.TransmissionShadow, Shadow.HairTransmittance, 1, 0, uint2(0, 0));
To this:
const float3 BsdfValue = HairShading(GBuffer, L, V, N, Shadow.TransmissionShadow, Shadow.HairTransmittance, GBuffer.CustomData.z, 0, uint2(0, 0));