Unity variables reset to zero C# Unity

I have the following code:

    private float defaultScale;

    public void Start()
    {
        defaultScale = (float)this.transform.localScale.x;
    }

The value of defaultScale can be printed in other functions such as

    public void increaseSize()
    {
        Debug.Log("Increase Size: " + defaultScale);
        if(!unlocked){
            return;
        }
        GameObject gameObj = GameObject.FindGameObjectsWithTag("medical")[0];
        gameObj.transform.localScale += specification/scaling;
    }

But it will reset to zero everytime when I call this function:

    public void BackToOriginalSize() {
        Debug.Log("Back To Original Size: " + defaultScale);
        if(!unlocked) {
            return;
        }
        GameObject gameObj = GameObject.FindGameObjectsWithTag("medical")[0];
        gameObj.transform.localScale *= (defaultScale/gameObj.transform.localScale.x);
        
    }

The actual value of 'defaultScale' doesn't change. It is just somehow BackToOriginalSize function can't access the value.

I got rid of the last two lines of BackToOriginalSize function and also tried calling it at different times, but all my efforts were unsuccessful.

I was wondering what's wrong with my code.

I don't really get the calculation or why you first store the original scale of this object (this.transform.localScale) but later go through FindGameObjectsWithTag .. or why you use the multiple objects poll at all if you only want the very first one anyway.

If those aren't in the same class then defaultScale might simply be never initialized and keep its default value 0.

I would simply do something like e.g.

private GameObject medical;
private Vector3 originalScale;

private void Start()
{
    medical = GameObject.FindWithTag("medical");
    originalScale = current.transform.localScale;
}

public void increaseSize()
{
    if(!unlocked) return;
      
    medical.transform.localScale += specification/scaling;
}

public void BackToOriginalSize() 
{
    
    if(!unlocked) return;
        
    
    medical.transform.localScale = originalScale;
}

Though in general this is probably rather something that should happen in a component of the medical object itself