They unknowingly stepped into a man in the middle type of attack to their system.
When they set the first two portals they were intercepted by the other civilization.
With the addition of the third portal they were triangulated in the multiverse foam and precisely located.
With the forth portal the stream between the portals was diverted to the attacker's destination. Each intercepted item is now being scrutinized to better assess the capabilities of our side and prepare countermeasures in case of an attempt of foul play.