Bought Chapter 4, load my end of Chapter 3 save and the credits come up straight away! Not Chapter 4! Had to go back to an earlier save replay 30 minutes of the game again, got to the end of Chapter 3 and this time, Chapter 4 loaded. A bug maybe?
I'm sorry you are having problems with the save.
If your savegame was from the -public edition- then that could be a problem but I would have to test that
You could try deleting the "persistent" file from the game's save folder and from the windows temp renpy folder->Game's name->Saves
Maybe send me your traceback.txt file and the save file so I can check it (itchv19games@gmail.com). But at that point I think is better for you just to start a new game and use the -ctrl- button with the "skip unread" option marked in the options until you reach the new content.