That's great! I had a feeling it was some sort of version incompatibility, but I had no idea where it came from, since I don't remember switching to Renpy 8 (specifically because I was worried about breaking the game).
Weird, but thanks for testing that out! I was planning to do it myself, but again - was hesitant about making the problem even worse.
EDIT: Now that I think about it, I may have done some debugging for Chapter 3 away from home and that could've been a newer version of Renpy... The dates match up.