I've seen theories that Janet or Michael was swapped when they got on the train to hand off the demon, with a Bad Janet/Vicki in a Michael suit.

I can see Janet's recent behavior being a disguised Bad Janet subtly sowing discord, and honestly would prefer if that arc had more going on than just Unknowable Immortal Beings Somehow Have Textbook Straight-Relationship Drama.

Would rather Michael be real, though. Especially since we've already done a whole season of "Michael is not who he seems to be." And his bonding with pseudo-Architect Eleanor is so rewarding, it would suck if a bunch of that turned out to be fake.