Hello
The preview button works with a custom application, with the "preflight" option checked.
We had problems using this solution. We couldn't find a reason but the update warning takes too much time to show. And my internet connection have a good quality and it's working fine.
It's not clear if the PREVIEW button updates all the content to the application, or only the selected content.
Anyway, Adobe has launched the Preflight application in Apple Store and Play Store. The Preflight APP works fine. The content that's not published can be viewed and approved.
I suggest you try the Preflight application.
Leo