Your batteries and receiver can easily pass 30 amps into a box that only will handle 10 amps continuous. When i tested some jr 8711 they would pull 5 amps not even starting to work hard..One stalled servo or a shorted pair of wires could have caused it to burn up. I would keep looking at the rest of the equipment in the plane. Most likely something else is going bad and the cortex was the weakest link