If you have webmail problems then you may have a bigger email issue but for Outlook 2016 ...
Have a look at which add-ins you have running. Lots are usually running by default. Most you do not need to have switched on unless you have a specific requirement to use them.
I have a dim recollection that one of them (maybe Exchange add-in or Social Connector add-in) may have caused a similar issue for me in the past on Outlook 2016.
Note down a list of what you have running to start with, then experiment by turning off one at a time to see if it improves anything for you. If that doesn't help you can always go back to your initial setup.