Adding Event listener Function through C# but still missing it

Question

I am getting strange behvaiour I don't know Why? I am adding function at Add listener on button click event but still its is missing as I reload my scene. I have this function. (Its getting desired button object correctly i have tested)

 public void SetupMenuSceneButtons()
    {
        if (GameObject.Find("BtnStartHost"))
            Debug.Log("BtnStartHost found");
        if (GameObject.Find("BtnJoinGame"))
            Debug.Log("BtnJoinGame found");

        GameObject.Find("BtnStartHost").GetComponent<Button>().onClick.RemoveAllListeners();
        GameObject.Find("BtnStartHost").GetComponent<Button>().onClick.AddListener(delegate { StartupHost(); });
        GameObject.Find("BtnJoinGame").GetComponent<Button>().onClick.RemoveAllListeners();
        GameObject.Find("BtnJoinGame").GetComponent<Button>().onClick.AddListener(delegate { JoinGame(); });

    }

I am calling above function on OnLevelWasLoaded event but its function assignment on click is still missing and my buttons are not working as i reload my scene. I have also tried Add event listener without delegate but same problem.

 GameObject.Find("BtnJoinGame").GetComponent<Button>().onClick.AddListener(JoinGame);

I have also tried assignment through this but still problem persist.

GameObject.Find("BtnStartHost").GetComponent<Button>().onClick.RemoveAllListeners();
        GameObject.Find("BtnStartHost").GetComponent<Button>().onClick.AddListener(()=> { StartupHost(); });
        GameObject.Find("BtnJoinGame").GetComponent<Button>().onClick.RemoveAllListeners();
        GameObject.Find("BtnJoinGame").GetComponent<Button>().onClick.AddListener(() => { JoinGame(); });

Answer 1

I ran a test of your code on v5.5, OnLevelWasLoaded is just not called and triggers a warning for being deprecated (funny it still autocomplete in VS).

The following is working:

 void OnEnable()
 {
     SceneManager.sceneLoaded += SceneManager_sceneLoaded; ;
 }

private void SceneManager_sceneLoaded(Scene arg0, LoadSceneMode arg1)
{
    SetupMenuSceneButtons();
}