Symfony form panel not showing in profiler

Question

I'm upgrading an old app in symfony 3.1 which was missing the forms panel after "Validation" panel on the left (it's the only missing panel). I thought that upgrading to latest 3.4.x (currently 3.4.18) would solve the problem. I've even deleted the whole vendor tree and installed from composer, but I don't get it to be on the web profiler though I see the "new" green bar and the version.

Any new projects or created by myself have it, so I don't think it's anything related to my installation. I've even compared composer.json to try to find out what could be missing, but I was unable to find anything useful. And the .../view/Collectors/form.html.twig file is there.

Here is my AppKernel.php:

use Symfony\Component\HttpKernel\Kernel;
use Symfony\Component\Config\Loader\LoaderInterface;

class AppKernel extends Kernel
{
    public function __construct($environment, $debug)
    {
        date_default_timezone_set('Europe/Paris');
        parent::__construct($environment, $debug);
    }

    public function registerBundles()
    {
        $bundles = [
            new Symfony\Bundle\FrameworkBundle\FrameworkBundle(),
            new Symfony\Bundle\SecurityBundle\SecurityBundle(),
            new Symfony\Bundle\TwigBundle\TwigBundle(),
            new Symfony\Bundle\MonologBundle\MonologBundle(),
            new Symfony\Bundle\SwiftmailerBundle\SwiftmailerBundle(),
            new Doctrine\Bundle\DoctrineBundle\DoctrineBundle(),
            new Sensio\Bundle\FrameworkExtraBundle\SensioFrameworkExtraBundle(),
            new Knp\Bundle\PaginatorBundle\KnpPaginatorBundle(),
            new Vich\UploaderBundle\VichUploaderBundle(),
            new Liip\ImagineBundle\LiipImagineBundle(),
            new Ikadoc\KCFinderBundle\IkadocKCFinderBundle(),
            new Core23\DompdfBundle\Core23DompdfBundle(),
            new AppBundle\AppBundle(),
        ];

        if (in_array($this->getEnvironment(), ['dev', 'test'], true)) {
            $bundles[] = new Doctrine\Bundle\FixturesBundle\DoctrineFixturesBundle();
            $bundles[] = new Symfony\Bundle\DebugBundle\DebugBundle();
            $bundles[] = new Symfony\Bundle\WebProfilerBundle\WebProfilerBundle();
            $bundles[] = new Sensio\Bundle\DistributionBundle\SensioDistributionBundle();
            $bundles[] = new Sensio\Bundle\GeneratorBundle\SensioGeneratorBundle();
            $bundles[] = new Symfony\Bundle\WebServerBundle\WebServerBundle();
        }

        return $bundles;
    }

    public function getRootDir()
    {
        return __DIR__;
    }

    public function getCacheDir()
    {
        return dirname(__DIR__).'/var/cache/'.$this->getEnvironment();
    }

    public function getLogDir()
    {
        return dirname(__DIR__).'/var/logs';
    }

    public function registerContainerConfiguration(LoaderInterface $loader)
    {
       $loader->load($this->getRootDir().'/config/config_'.$this->getEnvironment().'.yml');
    }
}

Here's a screenshot at login page, where there is a form:

What am I missing?