One more thing I forgot to mention. After I managed to get out of the locked room, I still couldn't go to the second floor. I just wandered around aimlessly until I suddenly could. I guess you need to check out literally every room one the first floor first, but they are all empty and pointless except the one from which you need to escape. So it would be better to just be able to go to the second floor immediately after you get out of the locked room with the piano. Maybe have some short dialogue after you get out of that locked room like "alright, there's definitely something weird going on here, maybe I should check the second floor now?"
Like this, I went immediately to that piano room and then thought that the game was bugged.