I really enjoy this game, the only thing I don't understand is why I have to completely start from the beginning every time I redownload it even after I save my progress. Can someone explain?
It depends on what is added in each update. This game will have multiple endings depending on your choices, so many variables are added to the scripts with each chapter, whenever the story requires it (Even new scenes get added). That is why sometimes your old savegame might have trouble finding new variables like new points with certain girls and relationship updates, thus resulting in script errors showing up during the gameplay. Because it is a game in development, and I'm still learning to use Ren'py I cannot guarantee that save games from previous updates will work. In fact, I test every update starting a New Game from scratch before launching them.
The good news is that the next update (Chapter X) will not have this issue with new variables and your savegame from Chapter 9 will totally work. Another good news is that the game is close to being finished, so you'll finally be able to play the game without the fear of what's coming next. Thanks for your comment, and I'm glad you like the game.
P.D.: The Skip (Not seen text) feature might be useful when starting a New Game to quickly skip the content you already saw while making the same choices you made in your last playthrough.