See what log files exist and may indicate when corruption first reported
For location of logs
https://support.plex.tv/articles/200250417-plex-media-server-log-files/
To repair/restore db
See
https://support.plex.tv/articles/201100678-repair-a-corrupt-database/
https://support.plex.tv/articles/202485658-restore-a-database-backed-up-via-scheduled-tasks/
