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'
Select 'Options'
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.
Select 'OK'