Symfony StopWatch events not appearing in profiler timeline

Symfony's profiler can't scan to code for all stopwatch instances and put that into the timeline. You have to use the preconfigured stopwatch provided by the profiler instead:

public function testAction()
{
    $stopwatch = $this->get('debug.stopwatch');
    $stopwatch->start('testController');

    // ...

    $event = $stopwatch->stop('testController');

    return $response;
}

However, your controller is already on the timeline...