Your itinerary is valid. The tool continues to have many bugs (and I personally find the AI version to be a real PITA ). You are still allowed four flight segments in Asia, even though it's your continent of origin, and up to two stopovers there.

You could try ticketing with the AA RTW desk. Not sure if they still require an AA-marketed "over water segment" (i.e. inter-continental segment), but if they do then fly AA LON-NYC (either AA metal or an AA codeshare on BA metal) or the AA codeshare on CX's NYC-HKG flights.

You only have 11 segments - leaving FIVE on the table! Not allowed here on flyertalk!