We have discovered the reason why the Outlook add-on is not working.
In the following picture, the bottom right hand corner of Outlook you will have new option called "Display Setting". Microsoft introduced a new feature to support 4K (high resolution monitors) and for computers supporting this resolution you will see that the "Display Setting" is set to "Optimize for best appearance".
Unfortunately this setting also can get in the way of add-on such as the Outlook add on from BeSoftware. If you change this setting to "Optimize for compatibility" you will find that the Outlook add-on will work for you as per usual.
Optimize for best appearance- This is the recommended mode for most users and it is the default. Office applications will be crisp as they move between monitors, but older add-ins and external code may have rendering problems.
Optimize for compatibility- If you're experiencing display issues, this mode will disable dynamic scaling for the current Office application. When dynamic scaling is disabled, text in the entire app may be blurry whenever the app is on a secondary display.
Some further information can be found at: https://support.office.com/en-ie/article/office-support-for-high-definition-displays-6720ca0e-be59-41f6-b629-1369f549279d
This “Display Setting” will only be visible on computers capable of running high resolutions (4K).