Search Results not showing correctly

I have a site that uses a custom search form and when there are multiple pages of the results, and I click on page 2, I get a 404 error – not found. Here’s the function PHP code:

if ($_GET['tags']!='') {
    function my_modify_main_query( $query ) {
        if ( $query->is_main_query() ) :
            if ($_GET['any']=='any') {
                $query->set('tag__in',$_GET['tags']);
            }
            else {
                $query->set('tag__and', $_GET['tags']);
            }
            $query->set('s', '');
        endif;
    }
    add_action( 'pre_get_posts', 'my_modify_main_query' );
}

If you perform a search, you will see what I’m saying – Try comedy tag since it has the most results if you want to see how the search is being done. http://romanceanimefans.com/blog