The only way it wouldn't show tickets is if there are no tickets with that user's user_id or if they are a collaborator on the tickets but you have the helpdesk configured to not show collab tickets.
- https://github.com/osTicket/osTicket/blob/develop/include/client/tickets.inc.php#L78-L95
- https://github.com/osTicket/osTicket/blob/develop/include/client/tickets.inc.php#L118
Cheers.