You won't be able to restore these assets unless you have a database backup. They were likely deleted by the database cleanup options found under Configuration/Scanning Setup/Server Options.
To prevent this issue in the future, either:
- Modify your settings under Configuration/Scanning Setup/Server Options.
- Prevent specific assets from being deleted by the Server Options by clicking the Assets link at the top of the web console, ticking the checkboxes in front of the assets, hitting the Mass Change button on the left and setting the "never delete by cleanup options" value to "yes" (ticked).
