Tags and Taxonomy links not working for Custom Post Types

I had to modify queries before they run. So the best practice was to add the following code to function.php:

if (!function_exists('my_theme_filter')) {
    function my_theme_filter( $query ){

    if ( $query->is_main_query() )
        if ( $query->get( 'tag' ) OR is_search() )
            $query->set( 'post_type', array( 'artprim_item' ) );

    //echo '<pre>'; print_r($query); echo '</pre>';

    return $query;
}}
add_filter( 'pre_get_posts', 'my_theme_filter' );

• if ( is_search() ) was necessary for taxonomy, this is what made this URL works :

  http://website.com/tax_groups/a_random_group/

  It’s surprising and made me lost a lot of time since the search by itself was already working just fine

• if ( $query->get( 'tag' ) ) obviously was necessary for

  http://website.com/tag/a_random_tag/