Health Bar NullReferenceException

I am trying to integrate a health bar system into my project. I have already got a script on my enemy that causes damage to my player on collision, and player health goes down correctly (which I can see via Debug.Log). However, for some unknown reason the Health Bar transforms straight to 0, and the text shows 0% after just one hit from the enemy. Any help would be much appreciated.

Code for HealthBar:

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

public class PlayerUI : MonoBehaviour {

	public static int playerCurrentHealth;
	public Text gameOverText;
	public Image currentHealth; //Healthbar
	public Text healthPercentText; //Healthbar

	void Awake ()
		playerCurrentHealth = gameObject.GetComponent<PlayerStats> ().playerMaxHealth;

	private void Start()
		UpdateHealthBar ();

	public void UpdateHealthBar()
		int healthPercent = playerCurrentHealth / (gameObject.GetComponent<PlayerStats> ().playerMaxHealth); 
		currentHealth.rectTransform.localScale = new Vector3 (healthPercent, 1, 1); //Needs fixing, health bar doesn't change!
		healthPercentText.text = (healthPercent * 100).ToString () + '%'; //Displays 100% but doesn't update!

Code for Enemy Damage:

	void OnCollisionStay(Collision attack) //Attacking the player
		if (attack.gameObject.tag == "Player" && PlayerUI.playerCurrentHealth > 0 && Time.time > enemyAttackTimer) 
			PlayerUI.playerCurrentHealth -= (gameObject.GetComponent<EnemyStats>().enemyDamage - GameObject.Find ("Player").GetComponent<PlayerStats> ().playerArmorRating);
			GameObject.Find ("Player").GetComponent<PlayerUI> ().UpdateHealthBar (); //This line is to call health bar function UpdateHealthBar
			Debug.Log ("You have been hit! Current Health: " + PlayerUI.playerCurrentHealth);
			enemyAttackTimer = Time.time + gameObject.GetComponent<EnemyStats> ().enemyAttackDelay;

EDIT: I had NullReferenceExceptions appearing on play, but had 2 of the same script attached to the player and one missing object references. Problem of health dropping straight to zero still persists.

I have absolutely no idea what was causing this! I re-wrote the code, and checked with the code posted above. No difference at all, except now it works?? Not complaining, but I’m bewildered… What could have caused that?