Just installed the game beta from Steam, and am having a problem with the game crashing when running using DirectX12 and alt+tab or switching window focus otherwise.  I found this post that recommended windowed mode which caused a slightly different behavior.  Instead of closing the game when switching to another window, it would close the game when bringing focus back to the game window.  I also tried settings seen on this post which did not change the behavior from regular windowed mode.

I'm running a multiple monitor setup and can add system information if it would be helpful.  DirectX11 works in both windowed and full screen.