Edit: it seems that just while writing this post that seat disapeared from CX, BA, etc availability. However I'm still curious on if the original issue where I could see availability for that flight, checking multiple times over the past week with it available. From your experiences was that most likely agent error and it was available, or was it likely that it was never available to begin with?

I'm trying to book a OneWorld award to get myself from SFO to Doha next month in business. I thought I was able to piece it together for a one world award on a combination of CX, QR, and RJ. When I called to book, they said that the QR leg from SIN-DOH is only showing available in economy. Searching on Asia Miles, it shows available in business. I also searched on the BA site and with Qantas, and both of those show the flight available (1 seat left) in business.

The routing I'm looking at is:
6/24 SFO-HKG-SIN (CX)
6/25 SIN-DOH (QR)
- 3 day stay in Doha, then revenue flight DOH-AMM on 6/27 -
6/28 AMM-BKK (RJ)
6/28 BKK-HKG-SFO

I'm not all that familiar with AM, this is my first AM booking. I'm wondering if the agent is wrong, or if trying to escalate or have them check directly with Qatar might show the availability? In searching, I've found that married segments play a lot into availability. For example I can book SFO-HKG-SIN but can not book SFO-HKG. My assumption is that since SIN-DOH is available as a direct flight, I should be able to build it into my OneWorld award. Is CX instead forcing their system to look at it as SFO-DOH and then married segment or routing logic kicks in to remove partner availability?