I always like to playtest Ren'py games before committing to a patreon for a very specific reason. The people using these engines tend to be artists, rather than developers. While I can appreciate the work that goes into the art, the lack of skill in programming tends to become glaring.
I would highly recommend you read the documentation for the engine you're using. It comes with a lot of valuable information that can help fix the issues you're encountering with your save files. Following tutorials on youtube is a bad way to learn an engine or language. It's fine to get you started but this is exactly what happens. I like this project but, personally, I can't support a game that lacks something as basic as a clean save.
I took a look at the save files and they are... interesting.. to avoid corruption I would suggest only saving in the map. Saving during a lot of the dialog will result in a broken save.