https://newbiedba.wordpress.com/2015/07/07/postgresql-missing-chunk-0-for-toast-value-in-pg_toast/
In some cases, it is possible that PostgreSQL tables get corrupted. This can happen in case of hardware failures (e.g. hard disk drives with write-back cache enabled, RAID controllers with faulty/worn out battery backup, etc.), as clearly reported in this wiki page. Furthermore, it can happen in case of incorrect setup, as well.
One of the symptoms of such corruptions is the following message: