Then the flaperon may have been lost during the late high speed gliding phase due to flutter, which may explain why it is the only larger piece of debris not totally torn to pieces during impact with the ocean.
There's a tendency to think that a high energy impact would have left a large floating debris field which may well have been spotted during the initial search phase. The fact that no debris was spotted leads to the thought that the aircraft may have sunk largely in tactwith the possible exception of the engines (which probably would have sunk) and the control surfaces exposed at touchdown.