Im also having the same problem and I suspect its been raised here but Im not sure if its exactly the same issue: Mouse lag since hotfix? - #4 by Kalahane-chogall
Either way, in my case this happens for 3rd reset day in a row - It sort of goes away after I play with the console commands for the mouse as suggested in the thread and then goes worse particularly on every Wednesday. No other game I play or out of wow situation has the same problem and I also reported it in-game (not sure if I will get a reply but havent so far). In fact, Overwatch where I am much more sensitive on how my mouse works has been just fine.