It‘s been like this for months and it is frankly unacceptable. The error may be on the AA side but these airlines are in the same alliance and are partners in a joint business. Both have their IT outsourced to different partners and I suspect that this is at the root of the issue here. Still no excuse of course, except that I suspect that either the governance over these providers is seriously lacking or that the cheapness of the arrangements entered into exclude appropriate recourse.

I suspect the JFK-LHR search from CWS succeeded due to the number of available BA options. The same search on AA.com reveals even more options. The reverse search for LHR-JFK will reliably error-out the whole time.