You should've kept more saves. It's common that a few of them will break when you update the game.
If you don't want to start over then install my mod and press the N of eterNum on the main menu 5 times to start from a chapter of your choice. If you then want to play without guidance you can disable my mod in the settings.
As a lesson for next time: Save often and in different slots! The best spots to save at are right after major scene transitions, those saves are most likely to survive game updates.