Why does my collider behave strangely after a coroutine

Question

So I'm trying to create a simple script that is going to handle the logic for cutting down a tree I'm experiencing some strange behaviour with my script.

I have a private field which holds the "HP" for the tree which starts at 100, and when I hit the tree it goes down by 25 every time, so I need to hit it four times in order for me to cut it down. Once the tree reaches <= 0 in terms of HP it should play an animation which simulates the tree being cut down, wait a couple of seconds and then play another animation of it appearing again. Most of this works fine, it's not until after the animation, where I start my CoRoutine to wait for a couple of seconds it starts messing up.

ISSUE

The first time I cut it down, it works fine.. However.. After it respawns I need to hit it like 4-5 times for it to go down to 50 health and then it works like normal. So I hit it once, it gets to 75, I hit it twice, still at 75, 3 times.. still at 75.. And eventually, it starts going to to 50, 25, 0 etc.. This only happens after I cut it down the first time, and the first time it works fine.

Here is my Tree script NormalTree.cs

public class NormalTree : MonoBehaviour
{
    public static NormalTree instance;
    private int health = 100;

    public Animator animator;
    private void Awake()
    {
        if (instance == null)
        {
            instance = this;
        }
        animator = GetComponent<Animator>();
    }

    private void Update()
    {
        if (health <= 0)
        {
            KillTree();

            
        }
    }

    private void KillTree()
    {
        StartCoroutine(TreeSleep());
    }

    IEnumerator TreeSleep()
    {
        animator.SetBool("treedead", true);
        gameObject.tag = "DeadTree";
        
        yield return new WaitForSeconds(3f);

        animator.SetBool("treedead", false);
        gameObject.tag = "Tree";
        health = 100;
    }

    public Item DamageTree(int damage)
    {
        health -= damage;
        Debug.Log($"Tree health {health}");
        if (health <= 0)
        {
            return new Item { Amount = 1, ItemRarity = Item.ItemRarityEnum.Gray, ItemType = Item.ItemTypeEnum.Log };
        }
        else
        {
            return null;
        }
    }
}

And in my PlayerController I have this, which essentially checks if my hitbox collides with an object that has the tag "Tree"

private void OnTriggerEnter2D(Collider2D other)
{
    if (other.CompareTag("Tree"))
    {
        var wc = Skills.FirstOrDefault(x => x.Name == "Woodcutting");

        var tree = other.GetComponent<NormalTree>().DamageTree(25);
        
        if (tree != null)
        {
            inventory.AddItem(tree);
            wc.AddExperience(25);
            Debug.Log(wc.Level);
        }
    }
}

Answer 1

You need to right away set health back to 100.

private void Update()
    {
        if (health <= 0)
        {
            health = 100;
            KillTree();

            
        }
    }

Your StartCoroutine(TreeSleep()); is being called n times per frame - since health < = 0 is true the whole time until the end of your Coroutine.