To shed some light into possible causes for it being a smaller update.
Codewise this game is awful. It seems whoever programmed the game had no previous experience with Python/Ren'Py or any object-oriented language or even C macros for that matter.
I'd think that a minor update for a month's work is a combination of artwork, programmer lacking experience and awfully written and bloated code (likely more work needed to implement new stuff in).
I also think the developer eventually saw their limitations and went for simpler minigames for book 4 (ala Candy Crush).
I've tried to clean up some of the code to fix some issues I was facing, but eventually decided to not bother at all with these unless it's a critical one.
The game needs to be rewritten from scratch by a programmer with some experience in OOP.
According to Patreon, they are making 20k$ a month, they could very well hire a programmer for this.