We have been getting some reports about empty collections in the latest build. We are not so sure what's happening yet, but if you do get the issue, try loading another collection and then reloading the old one.
Another issue that is causing your collection to blank out might be a corrupted card database, in which case you will need to delete and reinstall the app. Just be sure to backup any local files first with iTunes File Sharing.
- Tan Thor Jen