Appointments+ admin notification custom receiver not working

Hello dear Team !

I have a small issue :

I have a custom code in a side-plugin to control who will receive notification asking an admin to confirm an appointment.

That code is this :

add_filter('app_notification_email', 'wpmudev_app_custom_mail',10, 3);
function wpmudev_app_custom_mail($mails, $r, $app_id){

global $appointments;
global $wpdb;
$r = $wpdb->get_row( $wpdb->prepare("SELECT * FROM <code>ojKl098D_app_appointments</code> WHERE ID=%d", $app_id) );
$id_sommelier = $r->worker;
$sommelier = get_user_by( 'id', $id_sommelier );
$mails = ",,". $sommelier->email ."";

return $mails;

It worked until one of the last update of the plugin. I tried to find in the plugin code if something changed without any success.

Do you know where this might come from ?

Thanks a lot !