I found that using the mouse pad on the physical keyboard causes the display to clear in the same way as hitting the Windows key + d. I’m using the keyboard set to UK - Is the a bug or a faulty keyboard?
P
This is a feature and not a bug (useless feature in my opinion 
)
You can disable this if you want https://www.top-password.com/blog/disable-specific-windows-key-shortcut/
Thanks Biosham, the work around stopped the desktop from clearing every time I used the mouse pad 
I still wonder why the mouse pad did it in the first place but at least I can use the keyboard without fetching my app back every few minutes.
P