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.

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)