Continuity mistake: 3-10 "Invictus": Diana crawls through the pipe, which we were told at the outset is the only underground passage and is barely large enough for her to fit through. Yet after saving Vincent, she sends him back by the same route. He's twice her size and he's carrying the rescued baby, but somehow he manages to fit through.
Plot hole: 3-11 "The Reckoning": Vincent reveals the underground kingdom to Diana for what is meant to be the first time. But she was already there twice in the previous episode, which was definitely not shown out of chronological order. She was taken below by the helpers to meet with Father, and was there again at the end when Vincent christened his son "Jacob."