100% is the anticheat problem, sometimes your knockback is reduced because you registered your hit when you get hit at the same time and your velocity will be reduced by 60%, but the anticheat thinks ur cheating so he will undo your velocity and set you back to your place. The next time you get hit, the anticheat that sets you there thinks you are using insane anti knockback and keeps bugging you there....
if this happens frequently you can't even move well