It has been nearly two years since that old thread, so I would normally recommend you have this in your child theme functions.php file:

add_action('pmxi_saved_post', 'wp_all_import_post_saved', 1000, 1);

function wp_all_import_post_saved($id) {
    do_action('search_filter_update_post_cache', $id);
}

Which is different from you showed.

Are you saying that when you import a new post, it gains both of those categories? Or only in our search, but not the actual posts?

Thanks for letting me know. I will close this thread for now.