The cobbled swan case bug

When trying to do the main story quest the cobbled swan case, it will completely hardlock my game after beating the first set of venatori and attempting to open the double doors to continue. 

It appears if I reload from before the quest started I can redo it but the same outcome happens each time, doors open, nothing loads but an empty space, the game will then freeze if you enter a menu, and you can't reopen that autosave. This quest is the only main story quest I have left so I cannot bypass it or try and do any others instead. 

Has anyone else encountered/found a way around this as the game is now unplayable 40 hours deep into it.