Please be informed, you have to destroy all 3 X-Cons to clear the stage. Otherwise, the stage never ends.
This X-Con functions fleet-controller role which brings drones to battle place and orders attack command. It keeps moving away from your sight to alive.
X-Con's position is displayed as a red triangle mark in mini-map. Find and chase this fighter. This is the unique rule of the game and it's fun to play.