I searched the forum re my issue and found this thread. I have the same issue: Booked Cathay r/t from JFK via AA using AAdvantage points. Cannot book seats in advance. Called Cathay and waited over an hour to get a rep who told me that I cannot book seats until 24 hours before.

But unlike the others, I am One World status.... AA current Platinum and Lifetime Gold. I don't get it. 40 years of flying AA and One World, and now I have to worry that there is a good chance that I will be stuck in a middle seat. Not a happy camper.