Search returns no results after upgrading from v1.9.8.1 to v1.18.2. Browser console shows: 'Unable to prepare query: Table ost__search doesn't exist'.

The ost__search table was not created during the upgrade. Create it manually by copying the table structure from a working osTicket installation of the same version, then run cron to populate it with existing ticket data. The table is required for the full-text search indexing system.