I'm also having this problem.

I'm not running any overlays and I've disabled pretty much everything.

I'm running Windows 10 with a GTX970, dual monitor display.

Crashes HARD with borderless window, seems to behave itself more often with fullscreen or at least tends to soft crash to desktop. However, when I interact with the inactive monitor and then re-interact with FFXIV, the screen flashes black and I see my GPU hit 0% usage before spiking back up.

Something really weird is going on with the FFXIV client, DirectX 11, NVidia and multi-monitor displays. I really wish Square-Enix would address this issue before Stormblood.