My unity STOPS RESPONDING when this function is activated

So whenever I click play everything is fine however when I do something that calls this function:

 void SwapCards()
      {
          string Temp = "tmp";
          for (int i = 0; i < isSelected.Count; i++)
          {
              for (int j = i + 1; i < isSelected.Count; j++)
              {
                  if (isSelected[i] == true && isSelected[j] == true)
                  {
                      Temp = Peçass[i];
                      Peçass[i] = Peçass[j];
                      Peçass[j] = Temp;
                  }
              }
          }
          howManySelected = 0;
      }

the Unity engine stops responding. I've tried to comment this function out and the engine keeps running fine so this one is definitely the problem. What can I do to fix this?

Here's all the code where this function is involved for better context:

 private void Update()
      {
          TimeStep = FindObjectOfType<GridCreation>().timeStep;
          if (Input.GetKeyDown(KeyCode.P))
          {
              canMove = !canMove;
          }
  
          if (canMove)
          {
              if (!isRunning)
              {
                  StartCoroutine(AplicarMovimento());
              }
              
          }else { StopCoroutine(AplicarMovimento()); isRunning = false; }
          if (howManySelected == 2)
          {
              SwapCards();
          }
          AbrirHotbar();
          FillImages();
      }
  
  public void OnPointerClick(PointerEventData eventData) //Deteta os "clicks" no UI
      {
          for (int i = 0; i < Peçass.Count; i++)
          {
              Transform carta = Hotbar.transform.GetChild(i);
              if (carta == eventData.pointerCurrentRaycast.gameObject.transform)
              {
                  isSelected[i] = true; //A carta onde deu click fica "selecionada"  
                  howManySelected++;
              }
          }
      }
  
      void SwapCards()
      {
          string Temp = "tmp";
          for (int i = 0; i < isSelected.Count; i++)
          {
              for (int j = i + 1; i < isSelected.Count; j++)
              {
                  if (isSelected[i] == true && isSelected[j] == true)
                  {
                      Temp = Peçass[i];
                      Peçass[i] = Peçass[j];
                      Peçass[j] = Temp;
                  }
              }
          }
          howManySelected = 0;
      }

The Unity version I'm using is 2020.2.2f1

Thank you!