Finally, got it fixed.

If you're on Windows 10, download the Xbox app if you don't already have it installed, go into settings (little gear icon on the bottom of the left sidebar), click on the Game DVR tab, and turn it off.

Seems Windows 10 has a built in overlay for screen and video capture that interacts poorly with FFXIV. Dunno why all of a sudden it started acting up on mine, but turning it off fixed it.