Been having the same problem for months with every single booking bar one. Doesn’t matter if I use the saved card (Amex) or enter details fresh for any card, or if I’m logged into my BAEC account or doing it from a clean sheet. Each time it’s a laborious call to the gold line who sort things out well and as quickly as possible, but WHY!!! The one exception nearly caused me to fall off my chair….. but BA weren’t going to let me off so easily. The booking was made from inside my BAEC account, but it failed to pick up my status and wanted piles of dosh to select seats and blocked row 1. Another call to the gold line to sort it out.