Oddly, I haven't really run into any truly game-breaking issues with DX11 since it came out, other than the weird texture colour glitch that has since been fixed, and I've seen a small but good enough performance increase from it. I have a few minor ones though. My machine is a Ryzen 5 3600, nVidia 1050Ti, Windows 10 machine, with the latest nv drivers (512.77) rather than the Windows builtin ones.
In Grothmar for example, some trees have some grass around the base (one of the trees just north of the wave mark tree near the ooze waypoint) which will move around/glitch depending on the camera angle. No such weird movement in dx9.
Other grass and flowers that would move as you run through them, are static in dx11. (edit – Ah right, I see others mentioned this as far back as last november)
The breeze effect moving the grass doesn't seem as pronounced in dx11.
There's a strange lag when I drag some icon around on the screen (from inventory or bank), on dx11 it will be much behind the mouse cursor, while on the otherwise less performant dx9 that isn't noticeable.
I get a very noticeable jitter when I close a window with a preview in it (most Hero window panels, eg. Fishing), or more like about a 0.5 s stall. It doesn't happen on dx9 and is pretty easy to see when turning the Hero window on and off while running.