As @droch-aon says, this is something he’s experienced recently, with regard to his machine. (I hope that’s accurate, dro, that it hasn’t happened before.) In his case, it may well be a Windows 10 issue, but with yours please keep reading. 
I’m just another player, but I’m also a PC technician, and I’ve been tracking a number of these sorts of graphics issues since the Mounts and Movement Update. I also have been watching these errors from far back in the game’s history as they’ve cropped up from time to time.
The issue is more than likely within your graphics card’s settings, drivers or both.
Here’s an earlier thread I’ve been referring out for a while:
Pertinent info in the above thread: If your PC has on-board video in addition to your add-on Graphics Card, the best solution is to disable it. This can be accomplished in either your System BIOS, or through your Device Manager.
Good luck, please give feedback. I’m sure we can get this nailed, and get you back in the game.