Incorrect DrupalSettings are passed to the js.

The function field_group_field_group_pre_render pass settings for the elements js :

  // Add all field_group format types to the js settings.
  $element['#attached']['drupalSettings']['field_group'] = array(
    $group->format_type => $group->mode,
  );

Variable $group->mode returns 'default' instead of 'form' or 'view' options which are used in js code.

  /**
   * Implements Drupal.FieldGroup.processHook().
   */
Drupal.FieldGroup.Effects.processHtabs = {
    execute: function (context, settings, type) {
      if (type === 'form') {

Therefore all implementations of the Drupal.FieldGroup.processHook() don't work correct.