Caldavbackend not dispatching event es. '\OCA\DAV\CalDAV\CalDavBackend::updateCalendarObject'

Hi Everybody,
I’m facing a problem with evetDispatcher in caldavbackend.php, I think for some reason it is not dispatched.

I have new empty app that is listen for this event like so:

$eventDispatcher = \OC::$server->getEventDispatcher();
                function(GenericEvent $event) {
                    \OC::$server->getLogger()->debug('-- Event CalDavBackend::updateCalendarObject listened!! ');    

But nothing in log.

I’ve also made a simple phpunit test that dispatche event and it works, I can see debug message in log:

 $eventDispatcher = $this->container->getServer()->getEventDispatcher();
 $eventDispatcher->dispatch('\OCA\DAV\CalDAV\CalDavBackend::updateCalendarObject', new GenericEvent(
                'calendarId' => 1,
                'calendarData' => 'abcd',
                'shares' => 'sssssharessss',
                'objectData' => 'mydata',

Another working thing is listen to different event, for example when user password is change, it works and I see debug message in log:

                function(GenericEvent $event) {
                    \OC::$server->getLogger()->debug('-- Event PasswordPolicy::validate listened!! ');                                          

How can be possible?

Nextcloud version (12.0.5):
Operating system and version ( Ubuntu 16.04):
Apache or nginx version (eg, Apache 2.4.18):
PHP version (eg, 7.0):

Anybody can help me please?
Do you have any idea what am I missing?