Multiplayer combat calculations run across all the players' individual games which means they calculate differently and look for the wrong information from the other players.
Potential Fix:
Change the combat system to look into network players' unit and structure lists.
Push combat system calculations to server side for multiplayer as opposed to individual players.
Multiplayer combat calculations run across all the players' individual games which means they calculate differently and look for the wrong information from the other players.
Potential Fix: