Custom post type not showing in (most) VC blocks

Hi everyone,
hope someone could help me.
I created a plugin that registers a custom post type (‘siti’).

Added a filter in the plugin as below:

add_filter('pre_get_posts', 'query_post_type');
function query_post_type($query) {
if ( is_category() || is_tag() || is_home() && empty( $query->query_vars['suppress_filters'] ) ) {
$post_type = get_query_var('post_type');
if($post_type)
$post_type = $post_type;
else
$post_type = array('nav_menu_item', 'post', 'siti');
$query->set('post_type',$post_type);
return $query;
}
}

The custom posts are showing great, as well as the taxonomies archives.
On the homepage, however, the only Visual Composer box that shows the custom posts is the “Big Grid 3” by adding the custom post type in the filter.
If I add for example a “Block 4” nothing happens.

Anyone have an idea?

Installed plugin: Yoast SEO premium, Wordfence, Progress map, Social Buzz.

Thanks in advance,
Marco