I have the latest firmware update for both the transmitter and receiver and when you swipe down on the screen to get into the Mono, Mono+ (Safety Track} or Stereo modes the Mono+ and Stereo functions do not activate.  Tapping once, long press, double tap, does not matter.  I don't see anyone else having this issue.  Any ideas???

Maybe it's a case of a failed firmware update? Try contacting DJI Support if they could assist you.