Feature items block is broken

Stepd

• Go to https://integrated-latest.e-activesites.nl/admin/block/new?class=Integrated\\Bundle\\BlockBundle\\Document\\Block\\FeaturedItemsBlock
• Result: error 500

Error message

[2017-05-19 12:27:44] request.CRITICAL: Uncaught PHP Exception Symfony\Component\Form\Exception\InvalidArgumentException: "Could not load type "integrated_sortable_collection"" at /home/integrated-latest/vendor/symfony/symfony/src/Symfony/Component/Form/FormRegistry.php line 92

{"exception":"[object] (Symfony\\Component\\Form\\Exception\\InvalidArgumentException(code: 0): Could not load type \"integrated_sortable_collection\" at /home/integrated-latest/vendor/symfony/symfony/src/Symfony/Component/Form/FormRegistry.php:92)"}

Note: Symfony 2.8 upgrade is expected to be the reason