When signing out of your Apple ID, if Notability data has not finished syncing to iCloud, the data will be evicted. This could be due to insufficient storage or not allowing your data to finish uploading.
At this time, you can recover this data through Auto-Backup. If you don't want to enable Auto-Backup, make sure to manually export your notes from time to time.
If you have a Mac connected to iCloud and a Time Machine backup of that Mac, you may be able to find notes in that backup:
- Open Terminal via Spotlight Search or Launchpad.
- Copy and Paste this link into Terminal: open ~/Library/Mobile\ Documents/ZP9ZJ4EF3S~com~gingerlabs~Notability
- Press Return. Finder should open to the above folder where your Notability notes are stored in iCloud.