I find that international OLCI only works ~50% of the time, especially when flying to the US, so it's never surprising when this happens. Typically just extra doc checks and what not, and there's no rhyme or reason as to why one pax was successful and the other wasn't. Even if you were both able to get your BP's, you still have to see an AA agent at LHR to go through the security questions and get the sticker on your passport, so I wouldn't consider it too much of a hindrance.