How can I register a bundle in kernel after composer update and git merge in Symfony 4?

After a git merge I made a composer update to my project and I get an error message now:

Attempted to load class "OneupUploaderBundle" from namespace "Oneup\UploaderBundle". Did you forget a "use" statement for another namespace?

(1/1) ClassNotFoundException

Attempted to load class "OneupUploaderBundle" from namespace "Oneup\UploaderBundle". Did you forget a "use" statement for another namespace? in Kernel.php line 33 at Kernel->registerBundles()in Kernel.php line 449 at Kernel->initializeBundles()in Kernel.php line 133 at Kernel->boot()in Kernel.php line 196 at Kernel->handle(object(Request))in index.php line 37

I tried then to make composer install, but the error is still the same.

composer.json:

{
    "type": "project",
    "license": "proprietary",
    "require": {
        "php": "^7.1.3",
        "doctrine/annotations": "^1.8",
        "jms/serializer-bundle": "^2.4",
        "symfony/asset": "^4.0",
        "symfony/console": "^4.0",
        "symfony/dependency-injection": "^4.0",
        "symfony/flex": "^1.0",
        "symfony/form": "^4.0",
        "symfony/orm-pack": "^1.0",
        "symfony/serializer": "^4.0",
        "symfony/serializer-pack": "^1.0",
        "symfony/twig-bundle": "^4.0",
        "symfony/yaml": "^4.0",
        "twig/extensions": "^1.5",
        "vich/uploader-bundle": "^1.8"
    },
    "require-dev": {
        "doctrine/doctrine-fixtures-bundle": "^3.0",
        "easycorp/easy-log-handler": "^1.0.2",
        "symfony/debug-bundle": "^3.3|^4.0",
        "symfony/profiler-pack": "^1.0",
        "symfony/test-pack": "^1.0",
        "symfony/var-dumper": "^3.3|^4.0"
    },
    "config": {
        "preferred-install": {
            "*": "dist"
        },
        "sort-packages": true
    },
    "autoload": {
        "psr-4": {
            "App\\": "src/"
        }
    },
    "autoload-dev": {
        "psr-4": {
            "App\\Tests\\": "tests/"
        }
    },
    "replace": {
        "symfony/polyfill-iconv": "*",
        "symfony/polyfill-php71": "*",
        "symfony/polyfill-php70": "*",
        "symfony/polyfill-php56": "*"
    },
    "scripts": {
        "auto-scripts": {
            "cache:clear": "symfony-cmd",
            "assets:install --symlink --relative %PUBLIC_DIR%": "symfony-cmd",
            "security-checker security:check": "script"
        },
        "post-install-cmd": [
            "@auto-scripts"
        ],
        "post-update-cmd": [
            "@auto-scripts"
        ]
    },
    "conflict": {
        "symfony/symfony": "*"
    },
    "extra": {
        "symfony": {
            "allow-contrib": true
        }
    }
}

config/bundles:

return [
    Symfony\Bundle\FrameworkBundle\FrameworkBundle::class => ['all' => true],
    Symfony\Bundle\TwigBundle\TwigBundle::class => ['all' => true],
    Doctrine\Bundle\DoctrineBundle\DoctrineBundle::class => ['all' => true],
    Doctrine\Bundle\MigrationsBundle\DoctrineMigrationsBundle::class => ['all' => true],
    Symfony\Bundle\DebugBundle\DebugBundle::class => ['dev' => true, 'test' => true],
    JMS\SerializerBundle\JMSSerializerBundle::class => ['all' => true],
    Oneup\UploaderBundle\OneupUploaderBundle::class => ['all' => true],
    Oneup\FlysystemBundle\OneupFlysystemBundle::class => ['all' => true]
];