BlendTree Animations Not Working On Horizontal Axis

I'm creating a simple movement system using some really simple code. I'm using a 2d Freeform Cartesian Blend Tree to blend together my walking forwards/backwards and strafing left/right animations. The animations work except the ones on the horizontal axis. Whatever animations I put on the horizontal axis play the first frame and just loops the same frame over and over. Although if i hold both the vertical and horizontal axis down then the animation will play.

 void Update () {
         float horizontal = Input.GetAxis("Horizontal");
         float vertical = Input.GetAxis("Vertical");
 
         Animator anim = GetComponent<Animator> ();
         anim.SetFloat ("VelZ", vertical);
         anim.SetFloat ("VelX", horizontal);
 
     }