The user may have configured closed requests to be reopened under Advanced Portal Settings → Request Reopen Settings, but this may not work for specific requests. Therefore, please investigate whether a lifecycle is associated with the request. If not, verify whether the request reopen settings have been correctly configured for the selected status, as the request status could also be a custom completion status.
Steps to follow if a lifecycle is associated with the request:
Navigate to the lifecycle associated with the request under Setup → Automation → Lifecycle and select the lifecycle.
Check if there is a transition available from the closed status to the open status of the request.
If no transition exists, create one (without adding any action) and check if the issue persists.
If the issue remains unresolved, kindly reach out to support with all the relevant details.