If you use a cloud service, ensure that it is configured to make all Scrivener projects “available offline.” Incomplete synchronization is by far the most common cause of missing data.
Read our article on best practices for using Scrivener with cloud services:
https://scrivener.tenderapp.com/help/kb/cloud-syncing/using-scrivener-with-cloud-sync-services
Check Scrivener’s automatic backup settings to make sure they match the way you work. If Scrivener stays open for days at a time, an automatic backup that only runs when Scrivener closes won’t help much. Do not rely on a synchronization service as your only backup.
Have at least one backup that is under your exclusive control. If you’re a Mac user, configure a Time Machine Drive.