anyone know how to fix this weird flasihing on metahuman hair? this only happen after the game built, not happening in editor. Metahuman Hair Glitch - YouTube
From the looks of it, it appears to be switching between LODs based on the characters distance from the camera. The default MetaHuman hair LOD distancing is pretty aggressive, and it seems as if your camera isn’t in a fixed position but lags behind the character when moving which could explain this.
I’d try keeping the camera at a fixed location and seeing if it still has that issue. If not, then that’s the cause and you’ll need to tweak your hair LOD distances.