Unity freezes every time I run one specific scene

I have different scenes that work fine except when I reach one specific scene. The different thing about this scene is the scripts. A game manager script and a card script. (The game is a personnalized memory game based on the memory card game). Every time I reach that scene, Unity freezes and I can't play it nor load another scene (using a loadonclick script). I am new to Unity and this is the first real problem I found. Especially when this same scene used to work fine when I first finished it yesterday... Anyway, here is the script I am currently using

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

public class CardScript : MonoBehaviour {

 public static bool DO_NOT = false; 

 [SerializeField]
 private int _state;
 [SerializeField]
 private int _cardValue;
 private bool _initialized = false;

 private Sprite _cardBack;
 private Sprite _cardFace;
 private GameObject _manager;

 void Start() {
     _state = 1;
     _manager = GameObject.FindGameObjectWithTag("Manager");

 }

 public void setUpGraphics() {
     _cardBack = _manager.GetComponent<GameManager>().getCardBack();
     _cardFace = _manager.GetComponent<GameManager>().getCardFace(_cardValue);

     flipCard();
 }

 public void flipCard() {

     if (_state == 0)
         _state = 1;
     else if (_state == 1)
         _state = 0;

     if (_state == 0 && !DO_NOT)
         GetComponent<Image> ().sprite = _cardBack;
     else if (_state == 1 && !DO_NOT)
         GetComponent<Image> ().sprite = _cardFace;
 }

 public int cardValue {
     get { return _cardValue; }
     set { _cardValue = value; }
 }
 //50
 public int state {
     get { return _state; }
     set { _state = value; }
 }

 public bool initialized {
     get { return _initialized; }
     set { _initialized = value; }
 }

 public void falseCheck() {
     StartCoroutine(pause());
 }

 IEnumerator pause() {
     yield return new WaitForSeconds(1);
     if (_state == 0)
         GetComponent<Image>().sprite = _cardBack;
     else if (_state == 1)
         GetComponent<Image>().sprite = _cardFace;
     DO_NOT = false;
 }

}

The part that I changed a lot lately was the flipcard part because I had some trouble getting it to work, so I'm guessing the problem could be coming from there?