Howdy,
It is possible the “Portfolio” page is using a custom page template, which in turn uses widgets from a different sidebar (or no sidebar…)
1. Edit the “Portfolio” page
— If possible, that is.
2. Check under “Page Attributes” to see if there is a custom template used.
You can check for different sidebars under Appearance > Widgets. Some themes will have the Default Sidebar and us those widgets for most pages, but then have a few other Sidebars that get used in specific areas (like the Portfolio page.)
Anyway, there are a few clues. Let me know if you need more help.
Take care,
Paul