Error 404 on category page 2 / custom post type

I had a problem with my pagination when I trying to display posts of the custom post type energoplast_product. The problem is that i get a 404 NOT FOUND error if i visit another page than the first category page. Archives.php (example – Category.php) only shows content of type ”post”, but you can alter it to include custom post types. 

Try change the pre_get_posts filter.

// functions.php
function namespace_add_custom_types( $query ) {
  if( is_category() && empty( $query->query_vars['suppress_filters'] ) ) {
    $query->set( 'post_type', array(
              'energoplast_product'
            ));
    return $query;
  }
}

add_filter( 'pre_get_posts', 'namespace_add_custom_types' );