You could try uninstalling vJoy and SmartPropoPlus and see if that helps. They install a custom driver that sometimes conflicts when using a USB connected controller.
[Fixed]
I can confirm that joystick values in 8-bit format works with FPV Freerider! I'm using a Joystick library from Heironimus, he has two versions, the older one works with this simulator. However, the channels "Throttle" and "Rudder" do not register in the calibration menu. Using for example Z-axis and X-rotation for throttle and yaw works.