Ahh yes!
Thanks John!
Changed my code to this:
//Auto add and update Title field:
function my_post_title_updater( $post_id ) {
$my_post = array();
$my_post['ID'] = $post_id;
$my_post['post_title'] = get_field('kop');
//Unhook function to prevent infitnite looping
remove_filter('acf/save_post', 'my_post_title_updater', 20);
// Update the post into the database
wp_update_post( $my_post );
//Rehook function to prevent infitnite looping
add_filter('acf/save_post', 'my_post_title_updater', 20, 3);
}
// run after ACF saves the $_POST['fields'] data
add_action('acf/save_post', 'my_post_title_updater', 20);
and now it finally works again!
Thank you very much for guiding me to the solution John!
