From experience, I know that fast forward and backward don't always work after an update in the case of RenPy-based games.You can also make three saves. And play every update all of them. The first time you play the complete update and the next two you can use CTRL to fast skip in the game you already saw.
Another thing is that choices that seem optimal in a given version won't always be optimal in the new version.
I don't know this game, but in the case of the game it was based on, almost every update required not only playing the entire game from the beginning, but also revising the choices and actions taken.