Plugin still working?

Check this function

function my_website_wp_terms_checklist_args( $args, $post_id ) {
       $args[ 'checked_ontop' ] = false;
       return $args;
    }
    add_filter( 'wp_terms_checklist_args', 'my_website_wp_terms_checklist_args', 1, 2 );

https://wordpress.stackexchange.com/questions/61922/add-post-screen-keep-category-structure