Interesting. Perhaps it was a result of moving this piece to the trash and the sent recover command didn’t restore it (because of too late).
I do not remember, is PieceID logged, when it’s moved to the trash on info level?
Or there was a real piece lost, hashstore checked after piecestore.
I have a one more idea - could you please search one of the piece on your disk in the piecestore?
See how to convert a PieceID to the file: