It's been a while since I played it but I think I might potentially know your problem.
In Chapter 5 you have to combine the lesson you learned in Chapter 1 and ignoring the advice the game
has given you up til that point. Basically; collect all the notes and backtrack/search super carefully to gather all of
them before a certain event triggers. I think you need them all before the two halves of the party have their
conversation across the massive chasm on the second floor.