enemy twitches and stops following player after leaving range

i have an enemy that follows the player, but when the character is far away enough from it, it stops moving and starts twitching.

 using UnityEngine;
 using System.Collections;
 
 public class ExperimentalEnemy : MonoBehaviour {
 
         public Transform target; 
         public Transform Bullet;
         public int moveSpeed; 
         public int rotationSpeed; 
         public float maxDistance = 50f;
         public int HitBoxRadius;
         public ExperimentalDeath Damage;
         public GameObject MonstercatChar;
         public float Health = 10f;
         private Transform myTransform;
         public GameObject Char;
         public Animator Enemy;
         public GameObject Poof;
         void Awake() {
             myTransform = transform;
         }
         
         // Use this for initialization
         void Start () {
             GameObject go = GameObject.FindGameObjectWithTag("Player");
             
             target = go.transform;
 
             GameObject Go2 = GameObject.FindGameObjectWithTag("Bullet");
 
             Bullet = Go2.transform;
 
             Char = GameObject.FindGameObjectWithTag("Player");
             
             maxDistance = 20f;
 
             HitBoxRadius = 4;
 
             
 
 
         //Reference to DamageChar from the ExperimentalDeath.cs script
         Component Damage = Char.GetComponent<ExperimentalDeath>();
 
     }
     
     // Update is called once per frame
         void Update () {
             if (Health < 0.1) {    
                 EnemyDie ();
             }
             Debug.DrawLine(target.position, myTransform.position, Color.blue);
             
             //Look at target
             myTransform.rotation = Quaternion.Slerp(myTransform.rotation, Quaternion.LookRotation(target.position - myTransform.position), rotationSpeed * Time.deltaTime);
             
             if(Vector3.Distance(target.position, myTransform.position) > maxDistance) {
                 //Move towards target
                 myTransform.position += myTransform.forward * moveSpeed * Time.deltaTime;
             }
 
             if(Vector3.Distance(target.position, myTransform.position) < HitBoxRadius) {
             Damage.DamageChar(Random.Range(0.01F, 0.2F));
             Debug.Log ("Is Damaging " + Char);
             }
 
         if(Vector3.Distance(Bullet.position, transform.position) < HitBoxRadius) {
             EnemyDamage(Random.Range(0.01F, 0.2F));
             Debug.Log ("Is Damaging Enemy By" + Bullet);
         }
 
         }
  
     public void EnemyDamage (float amount) {
         Health -= amount;
     }
 
     public void EnemyDie () {
             Instantiate (Poof, transform.position, Quaternion.Euler(0f, 0f, Random.Range(0f, 360f)));
             Destroy (gameObject, 5);
             Enemy.SetBool ("Die", true);
     }
 
     void onTriggerEnter (Collider other){
         if (other == GameObject.FindGameObjectWithTag ("Bullet")){
             Destroy (other);
             EnemyDamage(Random.Range(0.01F, 0.2F))    ;
             Debug.Log ("Bullet In Range");
             Debug.Log ("Object in Range");
         }
     }
 
 }