After upgrading to Symfony 3.3.0 we realised, that when we had something like this:

     * @Route(
     *     "/c/{articleId}/",
     *     name="article_simple_no_alias",
     *     methods={"GET"},
     *     requirements={"articleId": "[0-9]+?"}
     * )

when I put into browser URL without trailing slash, I was redirected automatically to URL with trailing slash. And it worked also other way.

In profiler -> request -> parameters, I could see:

_controller	
"Symfony\Bundle\FrameworkBundle\Controller\RedirectController::urlRedirectAction"
permanent	true
scheme	null

It was ok. But since 3.3 version this feature is missing and we could not find it in changelog if it was change intentionally. Now the page without trailing slash is giving us error 404 and we really don't want to go through whole project and update all routes, so this trailing slash would be optional..