Do these three things first

  1. Reopen WPS — a Document Recovery pane usually appears with timestamps;
  2. If not, go to File → Backup and Recovery → Backup Management;
  3. Cloud documents can be rolled back from Version history.

Local cache

WPS keeps temporary files in a local cache folder; find its path under Settings → File Locations and sort by modified time for .bak files.

Prevention

Set auto-save to five minutes, keep important work in the cloud and enable "always keep a backup copy".