Notification comes once in a while

I have some trouble getting the notification to work when there has been activity on my Owncloud server.
I have set it to send an email every hour, when there have been new activities. It does not work.
There possibly may come a mail with the message there have been new activities, but it may take many hours before it comes.
I have tjeket mail setup, and it works as it should, no spam or something like that.
The cron job also works as it says: "Last cron job execution: Just now."
I have tried with other users where the same thing happens.

Owncloud version 9.1.3

Follow the troubleshooting methods for mail notifications:

Thanks for your reply.
I have error searched mail setup, and it works just as it should.
the problem is Ownclud not get sent an email with the new activities, although there is new entry in activity overview.