Hi, I get used Phantom DJI 3 Advanced from my friend, sow him flying.
  

I upgraded the firmware to V01.08.0080, and the "No Signal" or "Safe to Fly" (non-GPS) sign appears.

  

Sometimes I see the picture from the camera and sometimes don't.

  

   Is there a way to downgrade the firmware on the copter and the controller?

  

Is there another way to fix the problem?

So I think I solved the problem. I believe that it is a sequencing issue. By that, I mean the order that I start up the drone as described by dji. Before, I was starting the controller and then the drone while the phone was plugged into the controller and the above was happeneing. However, when I started them in the order recommended by dji, (1)power on ac, (2)power on rc, (3)open dji go  app and select P3A, (4)plug device into rc; I don't have "No Signal" warning and have the video feed.