The hair changes to black literally just by changing the view angle in UE5 (front is normal, side is pure black). What causes this? Hair is exported from Blender (not using any plugins). I use a copy of the MetaHuman hair shader. If I unplug everything from the shader, the behaviour stands. When I plug in a vector3 to the normal input, the behaviour changes (vertical stripes at 0s, more pinkish and brown hues instead of black at 0 0 1, stays the same at 0 1 0), but isn’t fixed no matter what value or hair attributes output I plug in.
I haven’t figured out the why of this issue, but I somewhat fixed it by recreating the tangent and normals by feeding this into my normal and tangent material inputs: ((VertexNormalWS + 0,1,0 into cross product) + VertexNormalWS into cross product) into derive tangent basis normal. Then RootUV into mask (R G) into DeriveTangentBasis UV. Plug the World Space Normal into the normal, tangent and anisotrophy inputs. Leads to consistent results from all sides:
And what seems to be the actual fix (but I’m not 100 sure it was that that fixed it) is that I changed curve type in Blender from stripes to strands and reexported. No artifacts now.