When a customer navigates to (Customer Portal > My requests > Closed requests), there are requests which Status is not closed but showing up in the list
Service Desk filters Open and Closed request based on the Resolution. If a request has a Resolution, it will be considered Closed and will show up in Closed requests. The Status of the request will not matter.
Clear the Resolution field of the request and it should show up in (Customer Portal > My requests > Open requests)