PC froze?!

So I'm using an RTX 2070, my cpu is a hexacore 2.6~5.0ghz.  16gb ram.  Not sure how relevant that is.
I have 3 displays, and normally I play oni on one display, put a movie or youtube on another, and have discord on the third monitor.  This has never been an issue before, however, while testing the DLC my game started getting incredibly sluggish, despite the fact I hadn't altered the map much.  I was on cycle 14 and had some outhouses, a research station, a super computer, 6 cots.

After the game became sluggish, I couldn't do anything on my pc at all.  I had to hold the power button down and restart it.  Feeling the chassis, it's not hot.  The temps seem fine, the CPU and GPU graphs are around 50% for each.   
I'm going to continue testing this, but it's happened already twice.  I may have to switch to a single display, though it sounds archaic.  
I don't know if this is some kind of memory leak.  It seemed like a GPU thing, but I have no real way of knowing that.