What might cause my "User error" in Watchdog?
This is not connected to the Token module.

You should not try to render a non existing entity. Your code should throw an exception instead:

use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;

  throw new NotFoundHttpException();


Or configure the route so that when you have a non existing entity as parameter in the route, drupal will throw this exception automatically. See the answer from Berdir to your last question:

https://drupal.stackexchange.com/a/205054/47547