C# Pause Menu Buttons not working in only 1 scene

Hi all, "semi new" to Unity and C#... let me just say that I went through about 60 different answer pages to try and find an answer before writing here! I also searched all over google for hours! (not kidding)

I have a very basic pause menu that I load in my 1st scene, which brings me immediately to my "hub scene", from there the menu works perfectly... i can load level 1 and 2 with no problems and the menu keep working as intented (I can change volume, go back to hub, quit application or resume)... everything works in hub AND level 1 and 2...

However, when loading level 3 which is a 2d space shooter (see unity tutorial space shooter as its very similar), the menu BUTTONS stops working... I can press ESC to open it... audio gets "dimmed"... mouse appears... I can close the menu again with ESC and game resumes perfectly... however none of the buttons on the menu works! Audio slider doesnt respond... and neither does any of the 3 buttons (quit, resume, return hub)... My "GUESS" is that since that scene has 1 coroutine with some yield and wait for second that could block the menu... i tried pretty much breaking that scene and removing as much as i could but nothing worked... menu doesnt want to work in that 1 scene...

Here is the full code from my pause menu (however i have re-written it 3 times with different syntax and sub functions and nothing changed) menu works in hub and in stage 1 and 2 but not in 3rd one...

THANKS to anyone who read this and many more thanks if you can help me out! :)

 using UnityEngine;
 using System.Collections;
 using UnityEngine.SceneManagement;
 using UnityStandardAssets.CrossPlatformInput;
 using UnityStandardAssets.Utility;
 using UnityEngine.UI;
 using UnityEngine.Audio;
 #if UNITY_EDITOR
 using UnityEditor;
 #endif
 
 namespace UnityStandardAssets.Characters.FirstPerson
 {
     [RequireComponent(typeof (CharacterController))]
 
 public class PauseManager : MonoBehaviour {
     
     public AudioMixerSnapshot paused;
     public AudioMixerSnapshot unpaused;
     [SerializeField] private MouseLook m_MouseLook;
     Canvas canvas;
 
     void Start()
     {
         SceneManager.LoadScene("HugoArcade");
         canvas = GetComponent<Canvas>();
         canvas.enabled = !canvas.enabled;
     }
     
     void Update ()
         {
             if (Input.GetKeyDown (KeyCode.Escape) && Time.timeScale == 1)
             {
                 canvas.enabled = true;
                 m_MouseLook.SetCursorLock(false);
                 paused.TransitionTo(.01f);
                 Time.timeScale = 0;
             }
             else if (Input.GetKeyDown (KeyCode.Escape) && Time.timeScale == 0)
             {
                 canvas.enabled = false;
                 m_MouseLook.SetCursorLock (true);
                 unpaused.TransitionTo(.01f);
                 Time.timeScale = 1;
             }
     }
     
     public void Quit()
     {
         Time.timeScale = 1;
         #if UNITY_EDITOR 
         EditorApplication.isPlaying = false;
         #else 
         Application.Quit();
         #endif
     }
 
     public void RTArcade ()
     {
         Time.timeScale = 1;
         SceneManager.LoadScene("HugoArcade");
         canvas.enabled = false;
         m_MouseLook.SetCursorLock(true);
         unpaused.TransitionTo(.01f);
     }
 
     public void ResumeGame ()
         {
             canvas.enabled = false;
             m_MouseLook.SetCursorLock (true);
             unpaused.TransitionTo (.01f);
             Time.timeScale = 1;
         }
     }
 }