Animation transitions are not always triggered with state change

I have a simple character controller script which I use to use WASD to move a character forward, backward and side to side. I then have an animation script that takes the WASD button presses and declares an animation state (0 = idle, 1-4 = up,down,left,right) which then triggers animations related to those directions.

This works, but often the character animations will transition to idle instead of going to the transition that the state change should dictate.

What do you think is going wrong to create this inconsistency? Scripts and screenshots below.

Player Movement Script

 using UnityEngine;
 using System.Collections;
 
 public class playerMobility : MonoBehaviour {
 
     public float speed;
 
     private Rigidbody2D rb2d;
 
     void Start()
     {
         rb2d = GetComponent<Rigidbody2D> ();
     }
     void FixedUpdate()
     {
         float moveHorizontal = Input.GetAxis ("Horizontal");
         float moveVertical = Input.GetAxis ("Vertical");
         Vector2 movement = new Vector2 (moveHorizontal, moveVertical);
         rb2d.AddForce (movement * speed);    
     }
 
 
 }

Player Animation Script

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class playerManager : MonoBehaviour {
 
 
     Animator anim;
 
     // Use this for initialization
     void Start () 
     {
         anim = GetComponent<Animator> ();
     }
     
     // Update is called once per frame
     void Update () 
     {
         if (Input.GetKeyDown (KeyCode.W)) {
             anim.SetInteger("State",4);
         } 
 
         if (Input.GetKeyUp (KeyCode.W)) {
             anim.SetInteger("State",0);
         } 
 
         if (Input.GetKeyDown (KeyCode.S)) {
             anim.SetInteger ("State",1);
         } 
 
         if (Input.GetKeyUp (KeyCode.S)) {
             anim.SetInteger ("State",0);
         } 
 
         if (Input.GetKeyDown (KeyCode.D)) {
             anim.SetInteger ("State",3);
         } 
 
         if (Input.GetKeyUp (KeyCode.D)) {
             anim.SetInteger ("State",0);
         } 
 
         if (Input.GetKeyDown (KeyCode.A)) {
             anim.SetInteger ("State", 2);
         }
 
         if (Input.GetKeyUp (KeyCode.A)) {
             anim.SetInteger ("State", 0);
         } 
     }
 }
 

Animator screenshot

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