I released version 0.0.4 of the RF9X_RK library to fix this problem. The RHHardwareSPI.cpp file calls SPI.begin() with no parameters, which initializes the SPI peripheral to use the default SPI SS pin, which is A5. Now it passes PIN_INVALID so it does not initialize the pin. RHSPIDriver initializes the CS pin that is passed to the constructor separately.
0.0.4 (2020-09-09)
- Modified the hardware SPI initialization to not set the default SS pin (typically A5) as an output and high, regardless of what was configured as the CS pin.