Issue #3325129 by Finn Lewis, LOBsTerr: Too few arguments for...

    // Overwrite the label and description for all displayed bundles.

    $media_type_storage = $this->entityTypeManager->getStorage('media_type');

    $group_type = $group->getGroupType();

    foreach ($this->addPageBundles($group, $create_mode) as $plugin_id => $bundle_name) {

      if (!empty($build['#bundles'][$bundle_name])) {

        $plugin = $group_type->getPlugin($plugin_id);

        $bundle_label = $media_type_storage->load($plugin->getEntityBundle())->label();

        $t_args = ['%media_type' => $bundle_label];

    foreach ($this->addPageBundles($group, $create_mode, $base_plugin_id) as $bundle_id => $bundle) {

      if (!empty($build['#bundles'][$bundle_id])) {

        $plugin = $group_type->getPlugin($bundle->getPluginId());

        $media_type = $plugin->getRelationType()->getEntityBundle();

        $media_type_label = $media_type_storage->load($media_type)->label();

        $t_args = ['%media_type' => $media_type_label];

        $description = $create_mode

          ? $this->t('Create a media of type %media_type in the group.', $t_args)

          : $this->t('Add an existing media of type %media_type to the group.', $t_args);

        $build['#bundles'][$bundle_name]['label'] = $bundle_label;

        $build['#bundles'][$bundle_name]['description'] = $description;

        $build['#bundles'][$bundle_id]['label'] = $media_type_label;

        $build['#bundles'][$bundle_id]['description'] = $description;

      }

    }