Hello, 

It's hard to say what exactly is causing the tickets to go missing. It could be that the ticket has been closed then deleted due to the Department deletion settings. Alternatively, it could be that the agent searching for the ticket does not have access to retrieve the ticket due to their group settings.

I would recommend submitting a ticket to our Support Department so they can review the specific examples and help you find a resolution. Unlimited standard support is included for any license that is covered by Maintenance and Support.  To submit a support ticket, please login to the SmarterTools website, click the account icon, and select My Tickets from the menu. 

Thank you,