FindWithTag returns null when looking for instantiated prefab

Questions & Answers
1

I have checked almost all related questions on the web and have not found the answer yet.

I instantiate an Enemy prefab mid-game and I want the Player to access the script attached to the instantiated Enemy object. Weirdly, I get a Null Reference Exception sometimes, not always. But I need it to work 100% of the time. This is the Player’s script where the error comes from:

var enemyObject : GameObject;
var enemyControllerScript : EnemyController;
var enemyHasEntered : boolean;
        
function Update()
{
	//Enemy object sets enemyHasEntered true in its Start()
	if(enemyHasEntered)
	{
		enemyObject = GameObject.FindWithTag("Enemy");
		if(enemyObject != null)
		{
			enemyControllerScript= enemyObject.GetComponent(EnemyController);
		}
		//enemyHasEntered = false;
		//I would ideally want to execute this section only once 
		//so repeated FindWithTag wont affect performance.
	}
	if(Input.GetButtonDown("Fire1") && Time.time > nextFire)
	{
		nextFire = Time.time + fireRate;
		Instantiate(bullet, bulletSpawn.position, Quaternion.identity);
		audio.Play();
		if(enemyObject != null)
		{
			enemyControllerScript.SlowMotionEffect();
//This is where I keep getting Null Reference Exception error whenever player fires. 
//I cannot access the SlowMotionEffect()of enemy script if FindWithTag fails.
		}
	}
}
2

This was a simple thing to solve but it took longer than necessary to come up with the solution. All I did was forced the player to keep looking for enemyControllerScript until it is found, like this:

function Update()
{
	//Repeat this until player finds enemyControllerScript
	if(enemyHasEntered && enemyControllerScript == null)
	{
		enemyObject = GameObject.FindWithTag("Enemy");
		if(enemyObject != null)
		{
			enemyControllerScript = enemyObject.GetComponent(EnemyController);
		}
	}
	.
	.
	.
}