swapped the sprite for my player character and multiple systems have broken (2D)

in my game I swapped the player sprite from the placeholder to the final design, and now i am encountering multiple issues

the boxCollider2D and the player double in size when i move left to right

the enemy has broken and no longer chases the player

I am receiving error NullReferenceException: Object reference not set to an instance of an object Enemy.FixedUpdate () (at Assets/scripts/Enemy.cs:34)

player disappears when I move left

the only thing I changed was the sprite under sprite renderer

the enemies code (error code is coming from here although no errors appear within visual studio

using System.Collections; using System.Collections.Generic; using UnityEngine;

public class Enemy : Mover { //Experience public int xpValue = 1;

 //logic
 public float triggerLength = 1;
 public float chaseLength = 5;
 private bool chasing;
 private bool collidingWithPlayer;
 private Transform playerTransform;
 private Vector3 startingPosition;

 //Hitbox
 public ContactFilter2D filter;
 private BoxCollider2D hitbox;
 private Collider2D[] hits = new Collider2D[10];

 protected override void Start()
 {
     base.Start();
     playerTransform = GameManager.instance.player.transform;
     startingPosition = transform.position;
     hitbox = transform.GetChild(0).GetComponent<BoxCollider2D>();
 }

 private void FixedUpdate()
 {
     //is player in range
     if (Vector3.Distance(playerTransform.position, startingPosition) < chaseLength)
     {
         if (Vector3.Distance(playerTransform.position, startingPosition) > triggerLength)
             chasing = true;

         if(chasing)
         {
             if(!collidingWithPlayer)
             {
                 UpdateMotor((playerTransform.position - transform.position).normalized);
             }
         }
         else
         {
             UpdateMotor(startingPosition - transform.position);
         }
     }
     else
     {
         UpdateMotor(startingPosition - transform.position);
         chasing = false;
     }

     //check for overlaps
     collidingWithPlayer = false;
     boxCollider.OverlapCollider(filter, hits);
     for (int i = 0; i < hits.Length; i++)
     {
         if (hits[i] == null)
             continue;

         if (hits[i].tag == "Fighter" && hits[i].name == "Player")
         {
             collidingWithPlayer = true;
         }

         // The array is not cleaned up, so we do it ourself
         hits[i] = null;
     }

     UpdateMotor(Vector3.zero);
 }

 public override void Death()
 {
     Destroy(gameObject);
     GameManager.instance.experience += xpValue;
     GameManager.instance.ShowText("+" + xpValue + " xp", 40, Color.magenta, transform.position, Vector3.up * 40, 1.0f);

 }

}