With FSO still off for WoW, can you guys all try disabling MPO and rebooting your PC, then try again? Yes, it’s an Nvidia link, but even AMD support will link it. It’s a part of Windows.
https://nvidia.custhelp.com/app/answers/detail/a_id/5157/~/after-updating-to-nvidia-game-ready-driver-461.09-or-newer%2C-some-desktop-apps
Download and run the disable one, then reboot. You can reenable it with the other if you want. I disable MPO on all the machines in our house because it causes issues with work related programs(UE editor menus bug out with it on sometimes and it gets annoying restarting the editor).
Also, another variable for me, that might be different for you, is that I globally enable VSYNC and disable it in games so that the global version controls it.
Also, if possible, can you get a frametime graph of it happening? Just use RTSS => options => refresh period=0 => check “enable frame time history overlay” and set it to graph => hit okay. Then make sure “show on screen display” is set to on and that “show own statistics” is set to on. It will give you a really accurate high speed frame time graph that can show single frame stutters even.