On the Original Prusa XL, communication with the peripheral boards (e.g. Dwarf board) is achieved using the MODBUS protocol. In MODBUS, there are two types of devices: the master and the slave, also known, respectively, as client and server. On Original Prusa XL firmware, the master is the XLBuddy, and each slave is called puppy.
A fingerprint is a unique identifier of a specific version of the firmware. The Original Prusa XL checks the fingerprint of the puppies, to ensure the firmware flashed on the peripheral boards is compatible with the printer, and the boards are safe to use. In case of a problem during this check, the printer will show the message: "Puppy # flashed fingerprint mismatch".
Error name: Puppy fingerprint mismatch
Error code: #17520
The error message will include the name of the puppy that has the fingerprint mismatch.
The firmware for all puppies is part of the Original Prusa XL firmware and bootloader files. Download the latest firmware and if necessary the bootloader relevant to your printer version, and flash the files.