[for (uint8_t i = 0; i < packet.length; i++) {](https://github.com/adafruit/Adafruit-Fingerprint-Sensor-Library/blob/358c6c9e439292923cace27128cd4d4191ed1ef4/Adafruit_Fingerprint.cpp#L518) Type uint8_t is max 255, our sending data length is 256, cycle is forever. So uint8_t change to uint16_t.