Seems like this is being resoved/has been resolved. I was able to book flights today that I couldn't yesterday as well
I called back in the evening and the agent was able to find space in coach and biz on AUH-ORD (both ways) for April dates I was looking at... However, I was pulling up the information from EY at same time and they quoted me availability on a few days with NO Guest Business and no availability on some days WITH Guest Business. Very strange.
Also I have still had no luck on PEK-AUH on Apr dates where EY showing Guest Business seats... I've been offered PEK-DOH-AUH on QR or PEK-HKG-DXB on CX as alternate options.