Task reminders do not remind me

I just switched from Outlook to eM Client and it works really good. But I have now a problem: I am working a lot with tasks and its reminders. But the reminders are currently not reminding me. They do not show a pop up or a sound. I checked the settings (Menu -> Settings -> Notification). The reminder option does not include the pop-up window option. Can anyone help me here?

Thanks!