So, wait -- your steps were as follows:
You clicked the ???
You watched a cutscene
You clicked the ???
You spawned, and subsequently killed Cetus.
You clicked the ???
You watched a cutscene
You clicked the Veridical Conflux
You watched a final cutscene
correct?
Or did you jump any step in between?
Edit: I also remember that stopped me at first, but I also clicked a ??? right next to the conflux and that triggered the CS before the Veridical Conflux.