I’m having a similar problem. Using WP V4.9.8, no other plugins. I can create a search form with categories and tags to select from, but when I click on the “Select” button, if I have not selected anything I get a partial screen with the message “Click to Continue”. Click then takes you back to the home page. If I select any category or tag and click on “Select”, some error messages flash up saying “no such item” or something to that effect, then the page goes black. Removing the search fields made no difference.