Originally Posted by
4BandE
It's just a mystery with no agent or supervisor able to give an explanation that seems reasonable.
That's not their job to explain why a seat swap happened - and I don't see UA training to that level simply because the swaps may not have an exact formula. At best I'd expect them to say - I'm not exactly sure why your seat was swapped, but we do see those situations in change of aircraft situations.
Their primary responsibility in this instance is to move you back to the seat you requested if you can't do it online or the app.