Entity field type disappear on server

I use an entity field type to represent Tags for Articles (many-to-many relationship). Everything is working as expected in local. However, when I connect to the Article form on the server (GoDaddy), the tags' checkboxes do not appear, only the name "Tags". Would you have any idea why?

Here is my form code:

$builder->add('tags', 'entity', array(
    'class' => 'WebArticleBundle:Tag', 
    'property' => 'name', 
    'multiple' => true, 'expanded' => true, 
    'query_builder' => function (\Web\ArticleBundle\Entity\TagRepository $r) { return $r->getDefaultTags(); }))

Here is an image of the missing checkboxes to makes things clear: