Found this on steam, and it worked for me for anyone else that comes across the issue:

"I was having the same issue for awhile now. It only happens when leaving the game when its fullscreen and using DX11. What fixed it for me was finding the ffxiv_dx11.exe in the game folder and right click it and under compatibility check "disable fullscreen optimization". Apparently this is a new Windows 10 feature that should optimize games and applications at the OS level but is known to have some issues.

Hope this helps you."