I used to have the Movement validation error in tree of savior, making it pretty much unplayable with all the backtracking, so i quit for a bit.
Then, while trying to solve lag problems for another game, it came to my attention that the ROG Game First 3 Service does exactly the opposite of what it’s suppose to do (reduce game lag/ping). And by disabling the service it magically fixed both the lag on that game, and to my pleasant surprise, the movement validation error/lag i was experiencing on TOS as well.
So for you ASUS ROG users out there, it’s worth disabling it just incase:
Task Manager > Services > AsusGameFirstService > (Rightclick) > Stop