Also had this happen to me for flights in September, after Labor Day. Tried to change my ticket booked on Aer Lingus to BA because I saw a ton of award space. The change was not processed (errored out) and I lost my Aer Lingus ticket in the process. Talked to Customer Service - they were extremely apologetic, promised to restore my original ticket (needed to be manually processed in their backend), but said that they are aware of issues with BA - they actually don't see much (if at all) availability in their internal system. They said that IT is looking at resolving the issue where the website is showing space that isn't there.