Impersonating ROLE_PREVIOUS_ADMIN not working

Partner.php

<?php

namespace Siu\AppBundle\Entity;

use Doctrine\ORM\Mapping as ORM;
use Symfony\Component\Validator\Constraints as Assert;
use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity;
use Symfony\Component\Security\Core\User\UserInterface;

class Partner implements UserInterface, \Serializable
{
    

    /**
     * @ORM\Column(type="text")
     * @Assert\NotBlank()
     * @Assert\Email()
     */
    protected $email;

    


    /* UserInterface */

    /**
     * @inheritDoc
     */
    public function getUsername()
    {
        return $this->email;
    }

    /**
     * @inheritDoc
     */
    public function getRoles()
    {
        return array('ROLE_PARTNER');
    }

    /**
     * @inheritDoc
     */
    public function eraseCredentials()
    {
    }


    /* Serializable */

    /**
     * @see \Serializable::serialize()
     */
    public function serialize()
    {
        return serialize(array(
            $this->id,
            $this->email,
        ));
    }

    /**
     * @see \Serializable::unserialize()
     */
    public function unserialize($serialized)
    {
        list (
            $this->id,
            $this->email,
        ) = unserialize($serialized);
    }

    
   
    /**
     * Set email
     *
     * @param string $email
     * @return Partner
     */
    public function setEmail($email)
    {
        $this->email = $email;
    
        return $this;
    }

    /**
     * Get email
     *
     * @return string 
     */
    public function getEmail()
    {
        return $this->email;
    }

    

    /**
     * Set salt
     *
     * @param string $salt
     * @return Partner
     */
    public function setSalt($salt)
    {
        $this->salt = $salt;
    
        return $this;
    }

    /**
     * Get salt
     *
     * @return string 
     */
    public function getSalt()
    {
        return $this->salt;
    }
}

security.yml

security:
    encoders:
        Symfony\Component\Security\Core\User\User: plaintext
        Siu\AppBundle\Entity\Partner: sha512
        Siu\PartnerBundle\Entity\User: sha512

    role_hierarchy:
        ROLE_ADMIN: [ROLE_ALLOWED_TO_SWITCH]

    providers:
        chain_provider:
            chain:
                providers: [admins, partners]
        partners:
            entity: { class: SiuAppBundle:Partner, property: email }
        admins:
            memory:
                users:
                    jleadmin: { password: foobar, roles: ['ROLE_ADMIN'] }

    firewalls:
        secure:
            pattern:    ^/
            anonymous:  ~
            provider: chain_provider
            switch_user: { role: ROLE_ADMIN, parameter: _partner_user }
            form_login:
                login_path:  login
                check_path:  login_check
            logout: ~

some.html.twig

{% if is_granted('ROLE_PREVIOUS_ADMIN') %}
    <a href="{{ path('default_home', {_partner_user: '_exit'}) }}">Never showed</a>
{% endif %}