Steps to reproduce:

1. Create an Article under the "Ibexa Platform" folder.
2. Create a custom URL alias with the following URL: /foo/bar/article.
3. Open a new incognito window in a browser and enter /foo URL.

Result:
One is presented with an exception:

Argument 1 passed to EzSystems\EzPlatformPageBuilder\Security\EditorialMode\TokenManager::create() must be an instance of Symfony\Component\Security\Core\User\UserInterface, string given, called in /Users/bartek/Projects/ezEE33/vendor/ezsystems/ezplatform-page-builder/src/lib/HTTP/Kernel/Fragment/DecoratedFragmentRenderer.php on line 196

Expected result:
A welcome page is rendered.