So apparently your fix introduced a bug when loading from saves at the end of the chapter (when the game asks if you want to save), when loading those saves the screen is completely black, you can move around and even go to the menus but you can't see anything and you're probably stuck.
What seems to be happening is that the game doesn't seem to like the changes made to the files and puts you on the map in which the chapter ends, I confirmed this because you can look at the in-game map when you load it and it puts me in the place in which we were when the chapter ended.
I managed to track down the file that was causing issues for one of those chapter saves and as you can see here:
https://www.diffchecker.com/6yaA4Smj
The only difference between them is the #Sound you added.
Honestly have no idea what could be causing this but replacing this file to uncomment the Sound commands does indeed fix that save.
Also seems like no other saves are affected, only the chapter saves, probably because of the special way in which they save the character positions.
I guess what I'll do is start looking for these files for all the chapters that have issues and post the fixed versions here later (this is pretty time consuming since I'm almost checking the file one by one since I have no clues about which files actually have the issue), unless you can think of a reason as to why this is happening.