Could you, please, tell me what is wrong with this hair mesh?
It looks normal in Blender and in the tool for modders(Wkit), but in the game part of the mesh is invisible.
Hair cards require two-sided shaders. Its an entirely on the engine side, and not the blender in general.
If there are any guidelines for this tool for making mods and hairs specifically in blender - check it. Maybe there is some specific way to predifine shader type by something like specific material name prefix or something like that.