As designed. The scenes reference different copies of the ScriptableObject. The first scene (init) is non-addressable and initializes a copy of the ScriptableObject (LOAD_SCENE_ADDRESSABLE) from the built-in scene data. The second scene (main_1) is addressable and references a copy of the ScriptableObject from the AssetBundle. This object is not initialized, and so its callback is null. To make both scenes reference the same object from the AssetBundle, make either the first scene (init) or the ScriptableObject addressable and load them as needed.