Oh you have a recent local backup? Well why not just use that!
When opening the file, there’s probably seemingly normal looking data, but a single line somewhere is excessively long and contains duplicate data tens of thousands of times. If you find it, it might reveal what caused it, but might not.
It would be good to figure out what caused the issue though, I’m guessing it was a module, but it’s strange that this started happening after gamesystem update, those are usually not a problem.