I have encountered this on numerous users' machines and found some seemingly reliable steps for fixing:
Setup for all users:
Windows 10, 1607 LTSB
Outlook 2016 (O365)
5. Close Outlook. In Windows, go to your Control Panel --> Programs and uninstall the Plugin. Reboot your machine and re-install the Plug-in.
This has worked in all cases I've come across of users having this issue