Hi Matthew,
it’s not a windows system shut down, it’s an instant power shutdown similar to when the cores are overheated and the pc is shutting down immediately to recover; however, I don’t get any windows’ error message (neither before the shut-down nor after I start turning on my windows again)… as I noticed that my 6 cores’ temperature are increasingly heating (from 30 to 75) when I start Unreal-Editor (beginning from the project selection window).
I’ve updated my AMD Video card drivers to the latest, and nothing changes :(.
but I believe this occurs when I do specific actions in the editor. like: baking lighting, tweaking with the materials (in real-time), compiling shaders, and Importing Assets. 
but I will try to get an error code this time, and I’ll shortly keep you posted.