same here. i try to get all available fields of a fieldgroup assigned to a specific post type:
$group_NAME = 'Attribute';
$the_query = new WP_Query( array( 'post_type' => 'acf-field-group', 's' => $group_NAME) );
$group_ID = $the_query->post->ID; // returns the valid ID !
$fields = array();
$fields = apply_filters('acf/field_group/get_fields', $fields, $group_ID);
but the $fields array is empty!