Strange issue.
Simple GetComponent() code works well in editor but simply returns null in build.
Code is executed when a player object gets instantiated into the game scene in Start():
GM =GameObject.FindWithTag("GameMaster").GetComponent<Game_Master>();
Debug.Log("" + GM.gameObject.name);
Control_Manager = GM.GetComponent<Player_Control_Manager>();
Debug.Log("" + Control_Manager.gameObject.name);
In theory this script should print the same name in both Debug.Log(). In Editor everything works. In build - the second Debug.Log() always produces null error.