itch.io

You kind of answered your own question. 'If done incorrectly.' If you edit it and it can't figure out how to run properly cause the value changed, a whole slew of things can go wrong. I'm no programmer, but I know a little. It all depends on how they made it. In this case I imagine they might have an anti-cheat in, which is fair. But it could also just be that when it attempts to read the save a ton of things go wrong and the save becomes corrupt.