This error is harmless and is not a sign of corruption in the slightest. The game just automatically gives each sim a relationship with themselves, most likely to prevent the sim from somehow meeting themselves in-game (can't remember where I read that, though). In short, it's something miniscule that HoodChecker registers as being a problem, at least from my understanding. I wouldn't worry about it too much
When a game is predictable, it's boring.
That goes for any medium that isn't life.
That's why The Sims 2 is my favourite sims game.
It has elements of unpredictability and everything feels more involved.
The Sims 4 is another story altogether...