Hi!
Thank you for the proper details, it helps me lot 🙂
I think I see the problem. You have the ‘Portfolio’ post type selected to be returned as results. However only the post title is selected to search, nothing else. I think you are looking to search by portfolio categories, so I have enabled this option, under the General Options -> Sources panel: https://i.imgur.com/XGHvyON.png
Now the plugin will return matches based on taxonomy terms (including portfolio categories).