I wouldn't be surprised if it doesn't cover that, I can imagine it'd be tricky to include without adding tens of bytes (10-20 bytes could be freed up by using slightly hackier function calls to/from the display, so perhaps Óscar will add more features/intelligence one day)

Was it a long castle? In that case, the squares the rook moves through don't block the move, it's only the squares the king moves through that block the castling move, so f8 and g8 for short castle and d8 and c8 for long castle.

Ah! It might have been that situation indeed, but I don't remember which square was attacked exactly. Good to know :)