In a Symfony 5.1.8 project I updated the httplug bundle to version 1.19.0.
It is mentioned in the changelog:
ConfiguredClientsStrategy no longer implements EventSubscriberInterface, this has been moved to ConfiguredClientsStrategyListener to avoid initializing the strategy on every request.
That results in an error in In
EventDispatcher.php line 270
Failed to create closure from callable: class 'Http\HttplugBundle\Discovery\ConfiguredClientsStrategy' does not have a method 'onEvent'