One board was faulty
I am using a board with 50 Ohm cupper sensor and the 3-wires connection, the board is connected to the Arduino Uno, 5V correspondingly., Adafruit_MAX31865_library. 1 ADC bit corresponds to 0.07 °C. Probably the sensor needs a calibration and the reference resistor should be lower twice. RTD value: 4251 Ratio = 0.12973022 Resistance = 55.91372680 Temperature = 30.33