Symfony version(s) affected: 4.4.9-dev, 5.0.9-dev, 5.1.0-RC1

Description
I'm testing my pet projects with Symfony 5.1 since the BETA1 release. I've upgraded them to RC1 today and the first thing I've noticed in each of them is that the debug toolbar is not displayed anymore. I can still access the /_profiler/ route, though. Rolling back to BETA1 solves the issue for me.

Update: The issue also happens on 4.4/5.0 if I switch to the latest dev packages.

How to reproduce

symfony new --full --version=next my_project
cd my_project
symfony serve

Possible Solution
Display the toolbar again. 😃