After the upgrade of 70 computers from Windows 10 1607 to Windows 10 1709 discussed in the previous post people started complaining about a lack of toast notifications coming from Outlook 2016.
And indeed. When checking the Settings app under "System -> Notifications & Actions" there were entries for all kinds of applications but no trace of Outlook 2016 anywhere. And checking a Windows 10 1607 machine showed that it had been there before the upgrade. So something broke with the upgrade to 1709, again ...