Users are not seeing all of their tickets in the portal

Users are not seeing all of their tickets in the portal

We have some of our customers that use the portal and they are reporting that they don't see some of tickets in the listing in the different sections. If they search for the tickets they are able to find them but they want them to be in the listing. Is there a way to control this or do you know what tickets show up in the list? Is there a way for me to go in and view the portal as a customer?
Thank you