according to this topic: Windowed Mode - resizing quits WoW - #71 by Tholaren-nordrassil
Blizzard changed some backend WoW code with 9.2, and now it’s highly unstable in MacOS (and it’s absolutely unusable in Windowed mode). Blizz says “not our fault, it’s a bug with macOS LOL”, even though literally NO other games or even applications bug out like WoW does, which means it’s a WoW-only issue (not a macOS issue). And now they’re refusing to fix this, or revert their code to the version that worked flawlessly.
Thanks, Blizz 