Error: Check the namespace prefix used with the resource

Shopware 6 (German) Installation / Einstieg
1

Bei einer bestehenden Installation hatte ich „leeren und Aufwärmen“ durchgeführt. Nun erscheint ein Fehler „InvalidArgumentException“

Expected to find class "App\Command\SystemGenerateAppSecretCommand" in file "/home/shop/src/Command/SystemGenerateAppSecretCommand.php" while importing services from resource "../src/", but it was not found! Check the namespace prefix used with the resource in /home/shop/config/services.yaml (which is loaded in resource "/home/shop/config/services.yaml").

Sowohl Frontend als auch Backend sind nicht mehr aufrufbar. Über das CLI kommt bei einem composer update auch dieser Fehler. composer dump-autoload kommen lauter „Warning: Ambiguous class resolution“.

Ich hatte auch schon mal alle Plugins deaktiviert, um zu sehen ob es daran liegt.

Wie kann ich die Installation wieder lauffähig bekommen? Bin für jede Hilfe dankbar.

> [ ! -f vendor/autoload.php ] || $PHP_BINARY bin/console system:update:prepare
Symfony\Component\Config\Exception\LoaderLoadException^ {#5666
  #message: "Expected to find class "App\Command\SystemGenerateAppSecretCommand" in file "/home/shop/src/Command/SystemGenerateAppSecretCommand.php" while importing services from resource "../src/", but it was not found! Check the namespace prefix used with the resource in /home/shop/config/services.yaml (which is loaded in resource "/home/shop/config/services.yaml")."
  #code: 0
  #file: "./vendor/symfony/config/Loader/FileLoader.php"
  #line: 174
  -previous: Symfony\Component\DependencyInjection\Exception\InvalidArgumentException^ {#5685
    #message: "Expected to find class "App\Command\SystemGenerateAppSecretCommand" in file "/home/shop/src/Command/SystemGenerateAppSecretCommand.php" while importing services from resource "../src/", but it was not found! Check the namespace prefix used with the resource."
    #code: 0
    #file: "./vendor/symfony/dependency-injection/Loader/FileLoader.php"
    #line: 224
    trace: {
      ./vendor/symfony/dependency-injection/Loader/FileLoader.php:224 { …}
      ./vendor/symfony/dependency-injection/Loader/FileLoader.php:105 { …}
      ./vendor/symfony/dependency-injection/Loader/YamlFileLoader.php:700 { …}
      ./vendor/symfony/dependency-injection/Loader/YamlFileLoader.php:256 { …}
      ./vendor/symfony/dependency-injection/Loader/YamlFileLoader.php:176 { …}
      ./vendor/symfony/dependency-injection/Loader/YamlFileLoader.php:132 { …}
      ./vendor/symfony/config/Loader/FileLoader.php:159 { …}
      ./vendor/symfony/config/Loader/FileLoader.php:98 { …}
      ./vendor/symfony/dependency-injection/Loader/FileLoader.php:66 { …}
      ./vendor/symfony/dependency-injection/Loader/GlobFileLoader.php:27 { …}
      ./vendor/symfony/config/Loader/DelegatingLoader.php:40 { …}
      ./vendor/shopware/core/Kernel.php:269 { …}
      ./vendor/symfony/framework-bundle/Kernel/MicroKernelTrait.php:171 { …}
      ./vendor/symfony/dependency-injection/Loader/ClosureLoader.php:39 { …}
      ./vendor/symfony/config/Loader/DelegatingLoader.php:40 { …}
      ./vendor/symfony/framework-bundle/Kernel/MicroKernelTrait.php:196 { …}
      ./vendor/symfony/http-kernel/Kernel.php:649 { …}
      ./vendor/symfony/http-kernel/Kernel.php:545 { …}
      ./vendor/shopware/core/Kernel.php:190 { …}
      ./bin/console:74 {
        › $application = new Application($kernel->getKernel());
        › $kernel->getKernel()->boot();
        › $application->setName('Shopware');
      }
    }
  }
  trace: {
    ./vendor/symfony/config/Loader/FileLoader.php:174 { …}
    ./vendor/symfony/config/Loader/FileLoader.php:98 { …}
    ./vendor/symfony/dependency-injection/Loader/FileLoader.php:66 { …}
    ./vendor/symfony/dependency-injection/Loader/GlobFileLoader.php:27 { …}
    ./vendor/symfony/config/Loader/DelegatingLoader.php:40 { …}
    ./vendor/shopware/core/Kernel.php:269 { …}
    ./vendor/symfony/framework-bundle/Kernel/MicroKernelTrait.php:171 { …}
    ./vendor/symfony/dependency-injection/Loader/ClosureLoader.php:39 { …}
    ./vendor/symfony/config/Loader/DelegatingLoader.php:40 { …}
    ./vendor/symfony/framework-bundle/Kernel/MicroKernelTrait.php:196 { …}
    ./vendor/symfony/http-kernel/Kernel.php:649 { …}
    ./vendor/symfony/http-kernel/Kernel.php:545 { …}
    ./vendor/shopware/core/Kernel.php:190 { …}
    ./bin/console:74 {
      › $application = new Application($kernel->getKernel());
      › $kernel->getKernel()->boot();
      › $application->setName('Shopware');
    }
  }
}
Script [ ! -f vendor/autoload.php ] || $PHP_BINARY bin/console system:update:prepare handling the pre-update-cmd event returned with error code 255