Originally Posted by jaytw

Yeah, I’ve noticed the same. It seems in some instances the flights will be available to book separately segment by segment, but not as a single one-way. The system will throw an error saying "Redemption Class Y not valid on this flight" or something to that effect. It did not start with the new search engine though, I think I ran into this as far back as May. The agent sees the same on their end, availability only available separately. The same routing was available to book on some other dates as a transfer, so it does not look like a blanket award routing rule thing. Also, FWIW, it’s not restricted to the CX search engine either, as availability for the same flight would not show up as a transfer in BA either, only segment by segment. It's perplexing because back in the day, it was usually the other way around, where transfer routing was available, but booking separately was not.

I did not HUCA, and just bit the bullet and booked separately, so I can't speak as to whether a different agent may have helped.

For data point purposes, my particular case was a TSA-HND and HND-LHR flight all on JL with a 17 hour overnight connection.