Did you update the iOS or Notebooks? - While none of these usually corrupt application data, it might be that something goes wrong during the update process (which cannot be influenced by Notebooks...)
- If you haven not done so, please try to restart your device
- If that does not help and you made a backup before the update, please try to restore your device from that backup.
- If that still does not restore your data, you might try to extract Notebooks' documents from that backup using one of the "backup extractor" applications that are available.
I hope this helps...