Hidden Voices appears to be broken for several characters in Act 2, with anyone not having a character paperdoll in act 3 having their talkChar value improperly updated. Ard becomes cmDefaultBoy instead of cmArd, the Lamia in the mountains retains the value of cmRobinThink or Talk from the previous line written, etc. Most of the time this results in NPCs having the "I shouldn't try to read minds while speaking its too confusing" or "I can't hear their voice, its like its muffled somehow." lines.
As a result some scenes like with the Lamia are actually locked off an inaccessible, while other scenes may still advance but the player won't be able to get the necessary context they should from hearing the character's normal thoughts.
Most of the housemates work, but this seems to be because they are the ones who have paperdolls. I suspect assigning talkChar based on the base image for the paperdoll is the problem. You should probably check that file, or just use a switch statement that checks characters' display names instead of doing anything too clever with image files. In programming clever is only clever until your foot has a bullet in it.