I noticed this a few days ago at the weekend as well (very frustrating), it seems to semi-impact ITA matrix as well (sometimes it does show CX, but seems to be expensive fares or not all routes). At the time I found examples on reddit implying that historically there was a 5-10 day blackout window in the past, subsequently fixed (I can't find the same thread again). Hopefully it is a temporary glitch and will be resolved - I still can't (HK based) search a simple HKG-SGN route in May and get a Cathay option for example.