Hello. Just an update - preview mode is not working at all at the moment. Any change to any card or layout, metadata, etc, isn't showing in the preview app. Even deleting and reinstalling doesn't work. And neither does deleting the app, signing a newly downloaded one from the DPS portal and refreshing. Everything is published. We have five collections in the main browse, and articles within collections. No cards or layouts are updating.
We just tried this locally and were able to change a card from black to red and see it in the preview app fine. Make sure you are pushing the preview button in the portal, not the publish button, after applying your changes.
If it still isn't working then you should contact enterprise support and they can assist further in figuring out why it isn't working for your project.