Thank you! This is going to be very difficult to debug then, maybe even impossible, but let’s try.
First, to make sure to rule out any misconfiguration related issues, please go to the Export/Import plugin submenu, and copy paste this to the import field.
Now if you go back to the main plugin menu a new search bar should be there named “test imported”.
This search we tested on all of our servers, and was returning items from the selected categories only. Go ahead, open it, and try it on the back-end preview window or place it’s shortcode to a frontend page. Do not change it’s configuration. Let me know how it goes.