"GameObject.FindWithTag" Working with one scene but not another

Hi guys,

I feel something strange is happening in one of my projects, I have this code bellow that works on one scene but not another, the one it doesn't work in is my main scene (and yes I have both tags). I'm not sure quite what to do, or if i'm doing something wrong, I have tried rolling multiplier in one room so that might be it, any suggestions please help.

 using UnityEngine;
 using System.Collections;
 
 public class testytest : MonoBehaviour {
     public GameObject map;
     // Use this for initialization
     void Start () {
         map = GameObject.FindWithTag("Map");
     }
     
     // Update is called once per frame
     void Update () {
         
     }
 }