I found the culprit in my case. My full-screen games kept minimizing at 30-40 minute intervals, and always twice in a row (about 2-3 sec apart). Usually right after I would click to maximize, it would minimize again. This cycle kept repeating (to my extreme frustration.. nothing like being in Battlefield and have your screen minimize right at a critical moment!).
The offender in my case was the "Akamai Netsession" services I had running in the background (loaded when Windows loads). Some SaaS platforms use this utility (i.e. Adobe CC Cloud, Autodesk, etc.) My task manager showed 2 separate instances running. Once I killed these, the issue stopped. Now made sense why my games would minimize twice in a row. I suppose the utility is set to pole something, however doing so takes exclusive control of the active desktop (whereby minimizing your game).
It's a little tricky killing them, as when killing one instance it is loaded back again by the other. So you have to be quick about it. I have reported this issue to Akamai, but I doubt they care.
Hope this helps others!