I've been witness to seat allocation arguments the last couple of times I've flown WTP from London to the US.

The combination of poor IT and poor communication makes it a really bad experience for people.

At least one I know was due to an equipment swap, because I'd been checking. That one turned out to be amusing onboard because someone ended up quite rudely confronting another passenger saying they paid for that bulkhead seat and who are you to make BA kick me out and give it to you. The person seated there replied that they'd actually paid for it too. Then they were accusing each other of lying about paying for it.