I might just be a glitch, try turn off the notifications feature for Outlook 2016 and then re-enable it to see if it helps. To do this, please follow:
1. In the search box, enter settings and then select the Settings app.
2. Go to System > Notifications & actions.
3. In Notifications & Actions, scroll down to Show Notifications from these apps and click on Outlook.
4. Set the notifications for Outlook to Off and then re-enable it.
5. Start Outlook and test the issue again.