The only important Disciples at this point (if we’re not counting Echo, Octavia, and Diyoza) are really Cadogan, Anders, Levitt, and Gabriel at this point, so my money is on Gabriel.
It would be a fun twist if Anders turned, however!
Based on the episode description and the trailer, I’m inclined to think that Gabriel “goes rogue” because he can no longer go along with the way Bill Cadogan runs things on Bardo, but preview material can be misleading. Still, I’m not sure Levitt has it in him to pull off any kind of elaborate plot, and I’m guessing he’s being used as leverage against Octavia.