Heya! Not, unfortunately this is still unresolved. Basically, if you have Lumen for Global Illumination and Reflections, you will get hair that half disappears, but is visible under certain angles. No amount of tweaking anything makes that any better.
If instead of Lumen you switch to…i think it’s called Screen Space (the one that says beta) will make the hair show up, but it makes it completely black.
The hair that kinda… shows up and collides with walls, I believe that was caused by the player camera, I don’t remember 100%, but check the collision. I remember I wanted to fix the camera going through walls (so you can kinda see outside the level), and fixing that also fixed the hair getting stuck on the wall.
The solution I am currently using until they fix their broken engine is faking the mirror by using the render to texture technique. There’s lots of tutorials on Youtube on how to make them, it’s basically another camera that will be streaming whatever it sees onto a texture, which can be a mirror (you might need to flip your UVs on the mirror’s model, you’ll see why once you implement it). I really hope they fix it, because I’m not looking forward to having my metahuman walk around any level with glass windows present xD
By the way, this issue has been present since 2020 apparently…