Drupal 8 : Render a field collection item in a Twig template
I've just started learning Drupal and encountered the same issue.
I solved it by creating custom field formatter:

public function viewElements(FieldItemListInterface $items, $langcode)
{
  $elements = array();
  foreach ($items as $delta =&gt; $item)
    if ($item-&gt;value !== NULL)
    {
      $builder    = \Drupal::entityTypeManager()-&gt;getViewBuilder('field_collection_item');
      $elements[] = $builder-&gt;build($builder-&gt;view($item-&gt;getFieldCollectionItem()));
    }
  return $elements;
}