Why I'm getting ArgumentException: failed to convert parameters when trying to load a scene?

Question

I have two scenes the first one and the one that is loading when running the game is main menu. The second scene is scene002.

I want to load scene002.

In the main menu scene I have a button. Attached to the button this script:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;

public class LoadSceneOnClick : MonoBehaviour
{
    private bool loaded = false;

    public void LoadByIndex(int sceneIndex)
    {
        SceneManager.LoadScene(sceneIndex);

        SceneManager.sceneLoaded += SceneManager_sceneLoaded;
    }

    private void SceneManager_sceneLoaded(Scene arg0, LoadSceneMode arg1)
    {
        if (arg0.isLoaded == true)
        {
            loaded = true;
        }
    }

    public void ActivatePlayer(GameObject player)
    {
        if (loaded == true)
        {
            player.SetActive(true);
        }
    }
}

When loading the scene002 i want to enable the Player.

In the button On Click I added to the list the two methods LoadByIndex and ActivatePlayer but when I click the button the player object I dragged to the inspector of the button is gone and I'm getting this exception:

ArgumentException: failed to convert parameters
System.Reflection.MonoCMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:484)
System.Reflection.MonoCMethod.Invoke (BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:528)
System.Reflection.ConstructorInfo.Invoke (System.Object[] parameters) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/ConstructorInfo.cs:77)
UnityEngine.Events.PersistentCall.GetObjectCall (UnityEngine.Object target, System.Reflection.MethodInfo method, UnityEngine.Events.ArgumentCache arguments) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:469)
UnityEngine.Events.PersistentCall.GetRuntimeCall (UnityEngine.Events.UnityEventBase theEvent) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:436)
UnityEngine.Events.PersistentCallGroup.Initialize (UnityEngine.Events.InvokableCallList invokableList, UnityEngine.Events.UnityEventBase unityEventBase) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:609)
UnityEngine.Events.UnityEventBase.RebuildPersistentCallsIfNeeded () (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:775)
UnityEngine.Events.UnityEventBase.PrepareInvoke () (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:811)
UnityEngine.Events.UnityEvent.Invoke () (at C:/buildslave/unity/build/Runtime/Export/UnityEvent_0.cs:53)
UnityEngine.UI.Button.Press () (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:36)
UnityEngine.UI.Button.OnPointerClick (UnityEngine.EventSystems.PointerEventData eventData) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:45)
UnityEngine.EventSystems.ExecuteEvents.Execute (IPointerClickHandler handler, UnityEngine.EventSystems.BaseEventData eventData) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/EventSystem/ExecuteEvents.cs:50)
UnityEngine.EventSystems.ExecuteEvents.Execute[IPointerClickHandler] (UnityEngine.GameObject target, UnityEngine.EventSystems.BaseEventData eventData, UnityEngine.EventSystems.EventFunction`1 functor) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/EventSystem/ExecuteEvents.cs:261)
UnityEngine.EventSystems.EventSystem:Update()

Answer 1

I suspect that scene loads successfully but your callback is giving you an error. Scene arg0, LoadSceneMode arg1 - might be wrong types.

But documentation says they are ok. https://docs.unity3d.com/ScriptReference/SceneManagement.SceneManager-sceneLoaded.html

So it is possible that you are passing wrong type in the inspector. Considering that it makes a call to Reflection it's probably related to serialization in inspector. Check out button event and correct the value if it's wrong.

EDIT

From the discussion with OP I understood that the problem lies in additive scene loading.

1. The problem was that the new scene was first loaded, losing all the data about previous scenes and then the button event tried to access that data.

2. A theory that references between 2 additive loaded scenes don't work in the inspector. (Will update the answer once I test it)