Gremlins aside, if the issue only just suddenly started happening, it could be something as trivial as a monitor cable degrading. It can happen that something as simple as a cable causes some graphical issues so its worth double checking that by using it in a different device and seeing if something similar happens.
If not or if that’s not possible, you can try to delete the three folders called WTF, Cache and Interface from your main WoW install folder. This will affect the addons you have installed however the main reason im asking you to do this troubleshooting is so that you can clear out the temporary game files that reside there. Once you delete the folders, try again with no addons installed for the time being and see if the issue continues.
If the issue continues then try to adjust the multisampling setting in the settings menu for WoW. Others with these graphics cards have reported some flickering textures and its an ongoing issue that is being investigated. No updates at this time for that which I do apologise. People have been able to fix it temporarily though by adjusting the multisampling to another setting, rolling back to a previous driver update or changing from DirectX 12 to 11.
Hopefully one of the above works out for you and I have listed them in order of things to try in an attempt to preserve the previous settings you had for the game. Regardless of the outcome, do let us know how it goes as if none of the above work it would be good to know for future troubleshooting for those with similar issues.