Safe Mode can be enabled to help stabilize Notability as a short-term solution in instances of performance issues such as crashing, freezing, or lagging.
Safe Mode disables Handwriting Recognition and Search, Auto-Backup, Audio Transcripts, and thumbnail previews. If thumbnails appear blank or have a spinning icon, it's possible that Safe Mode is enabled and causing this behavior.
To enable or disable: Device Settings > Notability > Toggle Safe Mode on or off.
Safe Mode is only available on iOS.