Sometimes Outlook stays on top of all other windows unless minimised. Here is a way to stop this happening.
To fix the Outlook issue where it stays on top of all other programs please do the following:
In Outlook go to 'File'
In the left hand menu select 'Add-ins' near the bottom of the list
Select 'Go...' at the bottom of the window
Find 'Outlook Social Connector 2016' in the list and untick the box next to it.