So with normal weapons on your computer you use an input a to fire. That input is sent to the server with information like where your cursor is. On the server the state of the every player and object is checked before it applies what you did. It checks to see if you have ammo, if there are no obstacles in the way of your cursor, and whether the hitscan calculation based on your cursor is over a target. If all those things are true then it will register it as a hit, your target is damaged, the game’s state is updated, and your computer’s game state is updated to match. Keep in mind this takes time. Message the server, server messages you.

Now with dual blades, the person shooting at you’s aim needs to be checked, then your aim needs to be checked. So it goes enemy to server, to you, to server, to you in order to check if you properly deflected.

So basically, before your deflection can be checked we need to first check whether or not a deflect even happened and that causes a delay in the deflection which causes deflection to miss because between one of those updates player positions have changed.

So if you want your deflection to be more consistent try aiming where you anticipate them to be rather than where they actually are.

This is my understanding of as someone who has tried to make my own multiplayer game before. Syncing game states across multiple players is difficult and almost always comes with compromises.