I 've set up my application to send my an email upon error with monolog so I've got some mails and try to confugure what the error was. There was lots of mails with the same error:
event.DEBUG: Notified event "kernel.response" to listener "Symfony\Component\HttpKernel\EventListener\StreamedResponseListener::onKernelResponse". [] []
It may be a very general type of error but I cannot understand what it means and I cannot find the corresponding documentation on error logging so I would be very grateful if anyone could help me about what this error means and when is it triggered.
This is not an error, this is a DEBUG log (as the first part of the line is event.DEBUG).
Monolog don't log only errors, but also warnings, infos, debug, etc... (see Psr\Log\LoggerInterface methods to see the full list).
In your case this is just a debug information that tell you that on the kernel.response event was triggered, and the Symfony\Component\HttpKernel\EventListener\StreamedResponseListener::onKernelResponse has been called to answer this event.