Yep this happened to me, too. I lowered Mayrina and she walks out of the cage but I can't talk to her and going into the hag's room does nothing because it's completely empty. Not sure what to do at this point.
Edit: I'm wondering if the reason why this got hosed is because I
1) went straight through the fireplace and didn't get entangled with the bloodthirsty goblin dudes
3) figured out that the door was fake without putting on one of her masks
2) snuck past all the thralled people with masks on and didn't engage with them either
Maybe if I hadn't tried to be sneaky and followed the script it would have worked? I don't know....
From the start, I told Mayrina that her brothers were dead outside. Then went through fireplace but fought the mask wearing folks. Figured out the fake door via Gale's arcana saving throw. Went down to where Mayrina is in the cage but no hag showed up. Mayrina kept telling me to burn the hag but nothing. Brought her down from cage then she doesn't talk with me.
I had restarted from the save when I was about to go through the fireplace. Same result. No hag. No Mayrina responding to talk.