Originally Posted by
Smirnoff
I suspect you will not get this kind of help and you will be told it was an "equipment change".
Thank you for the detailed explanation - this helps. As it turns out, it wasn't any of the conditions mentioned due to any changes. No changes had been made to any aspect of the booking (timing or ticketing).
Funnily enough, there is someone in the seat now, so I can't change it back. I'm guessing that someone really wanted the seat. I'm not really that bothered, but it's a bit disconcerting that selecting something beforehand is fairly susceptible to shifts even when nothing else has changed. It somewhat subverts the whole notion of the process.