I noticed this too. I was in the process of finalizing my plans of booking PVG-HKG on partner Cathay and Dragon Nov 22. Prior to yesterday, wide open availability basically everyday including Nov 22 (like 10+ seats open on 10+ flight options each day in Econ/Biz). As of yesterday, all of a sudden ba.com is either erroring out on my search query screen or it shows no availability for any flights PVG-HKG Nov 15-Nov 24. Strangely BA.com seems be able to search and displaying the right award space for PVG-HKG after Nov 25.
I just checked asiamiles.com for award availability on the PVG-HKG Cathay flight and it's still showing available with 6+ award seats in Biz. I called BA's telephone award desk to confirm availability and the phone agent confirmed BA.com is accurate, meaning she wasn't seeing any Avios award availability PVG-HKG Nov 15-24.
I ended up booking using my American Airlines miles for my desired PVG-HKG Nov 22 Biz Award flight. AA had no issues seeing the award space and the AA phone rep confirmed she was seeing 9+ Biz award seats on the Nov 22 PVG-HKG flight I ended up booking.
This must be a BA award search IT outage. Too bad since I just transferred 96k Avios from Amex MR last month and this flight would only cost 15k Avios vs 22.5k AA miles.