Experienced the following yesterday:
While booking some AY flights for me, our corporate TA put my AB FFN into the reservation.
When I tried to reserve seats I was able to without any charges but was not able to save the reservation - I was always requested to input my FFN but unable to select AB.
TH AY helpline entered the FFN manually but I got the same error when trying to reserve seats. In the end they reserved the seats manually for me.
Looks as if the OW benefits are slowly disappearing...