Why does using Buttons slow down scene loading?

So, I'm trying to load the next scene by pressing a button on screen. Earlier, I had it so when the user presses enter, the scene will load, but after realizing that wouldn't work too smoothly on iPads, I decided to switch to buttons. But the button method makes the next scene nearly two minutes to load, while the press Enter method was nearly instantaneous. Anyone have any idea why that is? //Press Enter method

 if (Input.GetKeyDown(KeyCode.Tab))
         {
             //If there's a space in the word, display a message and don't progress
             if (input.text.Contains(" "))
                 warningWord.text = "Words cannot contain spaces!";
             //If the word is valid...
             else if (!string.IsNullOrEmpty(input.text))
             {
                 //Display no error message
                 warningWord.text = ("");
                 //Set the string to the inputfield's contents
                 wordToSpell = input.text;
                 //Show the list of already typed words
                 typedWords.text = typedWords.text + "\n" + input.text;
                 //clear the input field
                 input.text = "";
                 //Set the word to all caps in order to keep it simple
                 wordToSpell = wordToSpell.ToUpper();
                 //Add the word to the list of words
                 wordList.Add(wordToSpell);
             }
 
             
         }
         //If the Return (Enter) key is pressed...
         if (Input.GetKeyDown(KeyCode.Return))
         {
             //If the user hasn't entered any words, display a message and don't progress
             if (wordList.Count == 0)
                 warningWord.text = ("You haven't entered any words!");
             //If the user has not selected a difficulty, display a message and don't progress
             if (!easy.isOn && !medium.isOn && !hard.isOn)
                 warningDifficulty.text = ("You haven't selected a difficulty!");
             //If a difficulty is selected and there are words that have been entered...
             if ((easy.isOn || medium.isOn || hard.isOn) && wordList.Count > 0)
             {
                 //Set the backup list to the real list
                 backupList = new List<string>(wordList);
                 //Set the difficulties depending on the selected bubbles
                 if (easy.isOn)
                     PlayerPrefs.SetString("difficulty", "easy");
                 else if (medium.isOn)
                     PlayerPrefs.SetString("difficulty", "medium");
                 else if (hard.isOn)
                     PlayerPrefs.SetString("difficulty", "hard");
                 //Make the canvas invisible as to hide the text boxes in the later scenes
                 canvas.gameObject.SetActive(false);
                 //Load the game
                 SceneManager.LoadScene(1);
             }
             
         }

//Button method

 void Update()
     {
         //As long as a difficulty is selected, don't display an error message
         if (easy.isOn || medium.isOn || hard.isOn)
             warningDifficulty.text = "";
         //If the enter word button is pressed...
         enterWord.onClick.AddListener(EnterButton);
         //If the start game button is pressed...
         startGame.onClick.AddListener(StartButton);
     }
     void EnterButton()
     {
         //If there's a space in the word, display a message and don't progress
         if (input.text.Contains(" "))
             warningWord.text = "Words cannot contain spaces!";
         //If the word is valid...
         else if (!string.IsNullOrEmpty(input.text))
         {
             //Display no error message
             warningWord.text = ("");
             //Set the string to the inputfield's contents
             wordToSpell = input.text;
             //Show the list of already typed words
             typedWords.text = typedWords.text + "\n" + input.text;
             //clear the input field
             input.text = "";
             //Set the word to all caps in order to keep it simple
             wordToSpell = wordToSpell.ToUpper();
             //Add the word to the list of words
             wordList.Add(wordToSpell);
         }
     }
     void StartButton()
     {
         //If the user hasn't entered any words, display a message and don't progress
         if (wordList.Count == 0)
             warningWord.text = ("You haven't entered any words!");
         //If the user has not selected a difficulty, display a message and don't progress
         if (!easy.isOn && !medium.isOn && !hard.isOn)
             warningDifficulty.text = ("You haven't selected a difficulty!");
         //If a difficulty is selected and there are words that have been entered...
         if ((easy.isOn || medium.isOn || hard.isOn) && wordList.Count > 0)
         {
             //Set the backup list to the real list
             backupList = new List<string>(wordList);
             //Set the difficulties depending on the selected bubbles
             if (easy.isOn)
                 PlayerPrefs.SetString("difficulty", "easy");
             else if (medium.isOn)
                 PlayerPrefs.SetString("difficulty", "medium");
             else if (hard.isOn)
                 PlayerPrefs.SetString("difficulty", "hard");
             //Make the canvas invisible as to hide the text boxes in the later scenes
             canvas.gameObject.SetActive(false);
             //Load the game
             SceneManager.LoadScene(1);
         }
     }`