see https://github.com/symfony/symfony/issues/19354

DomainUserParamConverter.php

<?php

namespace Application\Request\ParamConverter;

use Application\Domain\User\Model\User;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\ParamConverter;
use Sensio\Bundle\FrameworkExtraBundle\Request\ParamConverter\ParamConverterInterface;
use Symfony\Component\HttpFoundation\Request;

/**
 * @todo Remove this class once https://github.com/symfony/symfony/issues/19354 has been fixed.
 */
final class DomainUserParamConverter implements ParamConverterInterface
{
    /**
     * @var ParamConverterInterface
     */
    private $converter;

    /**
     * Constructor.
     *
     * @param ParamConverterInterface $converter
     */
    public function __construct(ParamConverterInterface $converter)
    {
        $this->converter = $converter;
    }

    /**
     * {@inheritdoc}
     */
    public function supports(ParamConverter $configuration)
    {
        return $this->converter->supports($configuration) || User::class === $configuration->getClass();
    }

    /**
     * {@inheritdoc}
     */
    public function apply(Request $request, ParamConverter $configuration)
    {
        if (User::class !== $configuration->getClass()) {
            return $this->converter->apply($request, $configuration);
        }

        // By setting the `convert_user` flag to false on a route, the param converter will be skipped entirely.
        // This will trigger the DomainUserValueResolver and return the User entity of the currently logged in user.
        // This is required, if route parameters may match a User entity but are not related to the resolution of it.
        if ($request->attributes->getBoolean('convert_user', true)) {
            return false;
        }

        try {
            return $this->converter->apply($request, $configuration);
        } catch (\Exception $e) {
            return false;
        }
    }
}

param_converters.yml

services:
    request.param_converter.domain_user:
        class: Application\Request\ParamConverter\DomainUserParamConverter
        decorates: sensio_framework_extra.converter.doctrine.orm
        arguments:
            - '@request.param_converter.domain_user.inner'
        tags:
            - { name: 'request.param_converter', converter: 'domain_user' }