I think that the nebula beyond Gamma Draconis was caused by the same phenomenon.
As far as the Shivan Juggernauts go, 82 Juggernauts, 6km long each with probably 30,000 Shivans on board each is one massive waste... with fighter and bomber squadrons stationed on board also. It was kind of a lame ending too. With 80 Sathanas's, they could have plowed through anything they wanted with little if any resistence.
What I think happened with the Ancients is that the knossos was closed between the nebula and Gamma Drac too late to save their civilization but stopped a Shivan colonization of the systems beyond it. Proof: Knossos 2 and 3 are open... why is knossos 1 closed until Bosche opens it? The means to open it are in Deneb. The Shivans probably have hundreds of knossos portals within their systems that were opened before their invasion and thats where they probably get their advanced subspace technology: Notice the shivan fighters have intersystem jump drives as well as intrasystem as shown in the fist encounter with the shivans at the knossos and at knossos 2.
I've spilled to much infor above Phi level clearance... I've been stripped of my rank and citizenship in the GTVA. I must go to my court martial and face my impending execution at 0700 hours. Later all.