I'm having this same problem on PS4...
I can't progress anywhere and the cutscene where it gives you the choice to either detain Florianne or confront her afterwards simply does not occur...
Most of the time, when I try to enter the Grand Ballroom, the game gets stuck on the black loading screen, and if it does load, no cutscene happens, the party is still ongoing, and Cullen is standing somewhere with Josephine next to the main door into the ballroom; there's no speech bubble above Cullen's head with which to interact with him at all, and the one above Josephine's head does absolutely nothing when trying to interact with her...also, when trying to enter the side-door into or out of the Grand Ballroom (the one leading back to the area where Florianne springs her trap on you), nothing happens at all...
This is ridiculous...
