On the Original Prusa MK4/MK3.9, the I2C bus is used for the xBuddy board to communicate with other printer components. In case of an unknown error with receiving data to the xBuddy board, the printer will show the message: "HAL detected an I2C undefined error when receiving data via I2C."
Error name: I2C Receive undefined
Error code: #13318 (MK4) #21318 (MK3.9)
Restarting the printer is expected to resolve the error, and this is not expected to occur again. In case a restart does not resolve it, please contact our customer support, we will take it from here.