The show starts off with the Breakout - a mysterious simultaneous failure of computer-controlled systems in all four super prisons. (The Mad Thinker had calculated it would happen, but did not himself take credit for making it happen.)
At least one of those prisons was "manned" by Ultrons. There was an unspecified security/containment breach in at least one of the others.
The Ultron we last saw had been programmed for violence, shown to be capable of interfacing with (and taking over) a computer system which was literally centuries ahead of its time, and specifically learned everything about the time drive that computer was designed to control.
Put it all together:
There is a distinct possibility that the Breakout was engineered by Ultron, using Kang's tech* to go back in time.
*The overuse of that word is one of the few things I don't like about this show. That and the way they draw Iron Man. Oh, and the way Tony, who is supposed to be such a genius, constantly needs Hank and Steve to figure things out and explain them. "Uh, right. JARVIS... what he said." But, other than Iron Man, I love this show.
I think it will be found to have been part of Lokis plan thus tying him to the avengers origin like the first book.There is the possibility that might be to obvious and there is a surprise coming to us on that count.