Ticket not appearing

A user has pointed out a problem. He was doing a search for resolved
tickets that he owns falling under a specific custom field value. The
ticket exists in the database and has the status of ‘resolved’.
However, entering the ticket number in the search box results in
nothing. Also, doing a search specifically for that ticket on the
Tickets page results in nothing again.

Is there an issue with v3.6.0 that might prevent some tickets from being
displayed or is this just, as my user called it, an RT anomaly? Or,
could something in the ticket get changed within the database which
prevents it from showing up in the UI?

Mathew Snyder