Hello,
I actually solved the problem. It was caused by using this function:
function namespace_add_custom_types( $query ) {
if( is_category() || is_archive() || is_tag() && empty( $query->query_vars['suppress_filters'] ) ) {
$query->set( 'post_type', array('post', 'prodotti', 'eventi', 'slideshow', 'nav_menu_item'));
return $query;
}
}
Enclosing the IF function in if(!is_admin()) { }
solved my problem.