Remove the following two lines from your sketch:
SPI.setDataMode(SPI_MODE3); // MAX31865 is a Mode 3 device
SPI.setClockDivider(SPI_CLOCK_DIV2);
The MAX31865 is a mode 0 or mode 3 device and sets it's internal mode automatically when you pull the CS pin low. After that you probably get correct results again.
Does that help?