Without more specifics it is rather difficult to advise here. But I'm guessing that this is someone with UK right of residence returning to the UK from North America, making some massive assumptions here. In which case the OP needs to check the API information and try again after half an hour or so. Particularly if there are clearly seats available in the cabin concerned, something that we could check from any information provided. It is worth calling up if on the outbound in this scenario due to ticketing factors, on the inbound there is probably very little that will be apparent to the contact centre agent. Maybe there is another airline leg before the BA one? And the PNR is shared over 2 people? In which case perhaps it's just the lead passenger's details that have come through as checked in.

Mostly it's a case of turning up at the airport and simply getting the boarding pass. The check-in agent probably won't see anything odd about the booking.