doctrine ManyToOne relation crashes symfony 3.3.1 - postgresql

Question

We have an old postgres 9.2 database with more than 400 tables. I used the symfony console to generate the entities, I created the repository classes that I need myself.
When I remove all relations from an entity, build a controller and repository to fetch some objects, everything works fine. But when I add a ManyToOne relation again symfony loads for about a minute or two and then I get a chrome error page "ERR_CONNECTION_REFUSED". Maybe someone can help.
AppBundle\Entity\Firma.php (shortened for better visibility)
namespace AppBundle\Entity;
use Doctrine\ORM\Mapping as ORM;
/**
* Firma
*
* #ORM\Table(name="firma", uniqueConstraints={#ORM\UniqueConstraint(name="firma_fid_key", columns={"fid"})}, indexes={#ORM\Index(name="IDX_2BED3563DF1BF902", columns={"ftypid"}), #ORM\Index(name="IDX_2BED35632453407B", columns={"hstraegerid"}), #ORM\Index(name="IDX_2BED356318F71675", columns={"hstypid"}), #ORM\Index(name="IDX_2BED3563950F9D92", columns={"uniid"})})
* #ORM\Entity(repositoryClass="AppBundle\Repository\FirmaRepository")
*/
class Firma
{
/**
* #var integer
*
* #ORM\Column(name="fid", type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="SEQUENCE")
* #ORM\SequenceGenerator(sequenceName="firma_fid_seq", allocationSize=1, initialValue=1)
*/
private $fid;
/**
* #var \AppBundle\Entity\Ftyp
*
* #ORM\ManyToOne(targetEntity="AppBundle\Entity\Ftyp")
* #ORM\JoinColumn(name="ftypid", referencedColumnName="ftypid")
*/
private $ftypid;
AppBundle\Repository\FirmaRepository.php
namespace AppBundle\Repository;
use Doctrine\ORM\EntityRepository;
class FirmaRepository extends EntityRepository
{
}
AppBundle\Entity\Ftyp.php (shortened for visibility)
namespace AppBundle\Entity;
use Doctrine\ORM\Mapping as ORM;
/**
* Ftyp
*
* #ORM\Table(name="ftyp")
* #ORM\Entity(repositoryClass="AppBundle\Repository\FtypRepository")
*/
class Ftyp
{
/**
* #var integer
*
* #ORM\Column(name="ftypid", type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="SEQUENCE")
* #ORM\SequenceGenerator(sequenceName="ftyp_ftypid_seq", allocationSize=1, initialValue=1)
*/
private $ftypid;
/**
* #var string
*
* #ORM\Column(name="ftyp", type="string", length=64, nullable=false)
*/
private $ftyp;
}