I personally doubt that this is the only way, but the bigger a save becomes, the higher the risk for corruption. OP on the forum has examples for how to make save files bigger, but basically: More builds, more sims, more functions (settings turned on), and just more of everything you could think of.
If you want to test out ( for science!) how the save corruption works, take a look at this new post about it on the forum.
The corruption comes from replacing lots basically, and mostly in Willow Creek. That's where it starts.
#thesims4
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