There are 2 demos inside the project, basically they have very identical code and structure. The difference is that for Demo 1, it uses Contract Names for the parent scene context and Parent Contract Names for the child scene context. But for Demo 2, it uses API to load

// moduleName is scene name
_sceneLoader.LoadSceneAsync(
    moduleName,
    UnityEngine.SceneManagement.LoadSceneMode.Additive,
    (x) => {},
    Zenject.LoadSceneRelationship.Child)

The outcome is that Demo 1 works great for binding reference to two child scene context while Demo 2 has issue on binding. Demo 2 binds reference fine for the first child scene context, but not the second(remaining ones).