UI policies are not applied to the Requested item when the request is submitted from the Service portal. It works as expected when the request is submitted from native UI.
The probable cause of the issue is using the deprecated SC Catalog item widget.
To resolve the issue, use the OOB widget. If you wish to use the custom widget, clone the latest 'sc catalog item' and add your customization to the cloned widget and use it in place of OOB widget instead of using the deprecated custom widget.