Broken precision using vec3 in struct, only on android webgl glsl (chromium)

Ray precision.frag.glsl

precision highp float;

struct TRay
{
	vec3 Pos;
	vec3 Dir;
};

vec3 ScreenToWorld(float2 uv,float z)
{
	float x = mix( -1.0, 1.0, uv.x );
	float y = mix( 1.0, -1.0, uv.y );
	vec4 ScreenPos4 = vec4( x, y, z, 1.0 );
	vec4 CameraPos4 = ScreenToCameraTransform * ScreenPos4;
	vec4 WorldPos4 = CameraToWorldTransform * CameraPos4;
	vec3 WorldPos = WorldPos4.xyz / WorldPos4.w;
	
	return WorldPos;
}

TRay GetWorldRay()
{
	float Near = 0.01;
	float Far = 100.0;
	TRay Ray;
	Ray.Pos = ScreenToWorld( uv, Near );
	Ray.Dir = ScreenToWorld( uv, Far ) - Ray.Pos;
	
	return Ray;
}

main()
{
  TRay Ray = GetWorldRay();
  //  Ray pos & dir seems low precision (varies based on angle in matricies, when w gets high)
  Ray.Pos = ScreenToWorld(uv, 0.01);
  Ray.Dir = ScreenToWorld(uv, 100.0) - Ray.Pos;
  //  now ray dir is fine!
  gl_FragColor = Dir;
}