Edit: This is for the problem where you reach the wellspring area inside the Traveler and no enemies spawn. It happened to me after I was in the mission in the next area after this, then got disconnected due to a server problem on launch day. After that, the enemies wouldn't spawn. This results in the mission being impossible to continue since you can't get the icon of darkness to open the door. The solution is to activate transcend. When you activate it, the enemies spawn. Then you can kill them and continue the mission. On Xbox, you activate it by pushing down both joysticks at the same time.