Inconsistent 2d collider hit registration

I'm working on a simple melee system and I'm getting very inconsistant hit registration. here is my Attack Trigger code

 using UnityEngine;
 using System.Collections;
 
 public class AttackTrigger : MonoBehaviour {
     public int dmg;
 
     void OnTriggerEnter2D(Collider2D col)
     {
         if (col.gameObject.tag == "Enemy")
         {
             col.gameObject.SendMessageUpwards("Damage", dmg);
             Debug.Log("Swing");
         }
     }
 }

Enemy code:

 public class Enemy : MonoBehaviour {
 
     public int health;
     // Use this for initialization
     void Start () {
     
     }
     
     // Update is called once per frame
     void Update () {
         if (health <= 0)
         {
             Destroy(gameObject);
         }
     }
 
     public void Damage(int damage)
     {
         health -= damage;
         //gameObject.GetComponent<Animation>().Play("name");
         Debug.Log("Hit");
     }
 }

Player attack code:

 public class PlayerAttack : MonoBehaviour {
 
     Rigidbody2D rbody;
     Animator anim;
     public Collider2D hitbox;
     private bool Attacking = false;
     // Use this for initialization
     void Start () {
         rbody = GetComponent<Rigidbody2D>();
         anim = GetComponent<Animator>();
         hitbox.enabled = false;
     }
     
     // Update is called once per frame
     void Update () {
         if (Input.GetMouseButtonDown(0))
         {
             if (!Attacking)
             {
                 hitbox.enabled = true;
                 anim.SetTrigger("Attack");
                 Attacking = true;
             }
             else
             {
                 Attacking = false;
                 hitbox.enabled = false;
             }
         }
         else
         {
             Attacking = false;
             hitbox.enabled = false;
         }
     }
 }

Here's a visual gif of whats happening https://i.gyazo.com/28f584c42cb0c33c447d6e6de50d813c.gif

Thanks for any help.