Aeroapi flights/search/advanced does not include origin.code_icao

I’m searching for flights by departure time and a lat/long bounding box. Flights are returned, but about 30% of them are missing the ICAO code for the departure aerodrome. This seems strange as the city (Gabarone) is correctly identified. Is this a bug? Or is there some other explanation for it. It really limits the usefulness of the API.

https://aeroapi.flightaware.com/aeroapi/flights/search/advanced?query={<%3D+hiLat+-18}+{>%3D+lowLat+-26}+{<%3D+hiLon+30}+{>%3D+lowLon+20}+{>%3D+actualDepartureTime+1733087400}&max_pages=100

[{“foresight_predictions_available”:false,“ident_prefix”:null,“last_position”:{“altitude”:35,“fa_flight_id”:“ZSMOC-1733149652-adhoc-3438p”,“update_type”:“A”,“heading”:242,“altitude_change”:“D”,“latitude”:-24.54305,“groundspeed”:140,“longitude”:25.94325,“timestamp”:“2024-12-02T14:29:49Z”},“bounding_box”:[-24.49722,25.94325,-24.54305,26.03846],“ident”:“ZSMOC”,“origin”:{“code”:“L -24.49722 26.03846”,“city”:“Gaborone”,“timezone”:“Africa/Gaborone”,“code_icao”:null,“airport_info_url”:null,“name”:null,“code_iata”:null,“code_lid”:null},“destination”:null,“aircraft_type”:null,“ident_iata”:null,“ident_icao”:null,“predicted_on_source”:null,“predicted_out_source”:null,“predicted_in_source”:null,“waypoints”:,“actual_off”:“2024-12-02T14:28:12Z”,“predicted_off”:null,“fa_flight_id”:“ZSMOC-1733149652-adhoc-3438p”,“actual_on”:“2024-12-02T14:29:49Z”,“predicted_in”:null,“registration”:“ZS-MOC”,“predicted_out”:null,“predicted_off_source”:null,“first_position_time”:“2024-12-02T14:27:27Z”,“predicted_on”:null}]