EntityEmbedDialog::buildForm leads to LogicException: The database connection is not serializable.

When I click in the editor on the Embed Button, only 'loading...' appears and the watchdog gives me this message:

LogicException: The database connection is not serializable. This probably means you are serializing an object that has an indirect reference to the database connection. Adjust your code so that is not necessary. Alternatively, look at DependencySerializationTrait as a temporary solution. in Drupal\Core\Database\Connection->__sleep() (line 1300 of core/lib/Drupal/Core/Database/Connection.php).

I also tried this with a clean installation of the standard profile.

Unfortunately, I was not able to find a solution as I do not understand where the problem comes from.

Maybe this issue is related to this problem: www.drupal.org/node/2475483

When I try to open the same form under /entity-embed/dialog/entity-embed/full_html/node
it shows more information:

serialize(Array)
Drupal\Component\Serialization\PhpSerialize::encode(Array)
Drupal\Core\KeyValueStore\DatabaseStorageExpirable->setWithExpire('form-ofHuE-S3ADdeISzndvQhZroFH29jY8RvRjdFz5jqZ1w', Array, 21600)
Drupal\Core\Form\FormCache->setCache('form-ofHuE-S3ADdeISzndvQhZroFH29jY8RvRjdFz5jqZ1w', Array, Object)
Drupal\Core\Form\FormBuilder->setCache('form-ofHuE-S3ADdeISzndvQhZroFH29jY8RvRjdFz5jqZ1w', Array, Object)
Drupal\Core\Form\FormBuilder->processForm('entity_embed_dialog', Array, Object)
Drupal\Core\Form\FormBuilder->buildForm(Object, Object)
Drupal\Core\Controller\FormController->getContentResult(Object, Object)
call_user_func_array(Array, Array)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1)
Stack\StackedHttpKernel->handle(Object, 1, 1)
Drupal\Core\DrupalKernel->handle(Object)