Tonight I flew .34 miles from “home” and lost “downlink”, usually for short periods (probably due to many trees between me and the P3A).  It was surely NOT a line of sight, but rather a FPV flight.  Finally, I lost contact for more seconds than I was comfortable with, and when it came back, it had been hovering.  I hit RTH and brought it home with no problem.

  

When I reviewed the flight log, it claimed “Downlink Restored (after 0m 10.4s)”.  Why didn’t RTH activate by itself?  I have it set to if signal is lost… but it did not.  

  

There are two signals.
One is the downlink (Phantom to controller) that carries your video and telemetry for the app.
The other is the control signal (controller to Phantom) that you use to control the Phantom.

It's common for the downlink to be lost earlier than the control signal.
In your case you still had full control signal and could have brought the Phantom back yourself, or use RTH as you did.
The Phantom will not initiate RTH until it loses control signal for 3 seconds.
You can tell if you have control signal by looking at the red/green LED on your controller.

labroides@yahoo Posted at 2016-7-28 07:37
There are two signals.
One is the downlink (Phantom to controller) that carries your video and telem ...

Thank you so much.  There sure is a learning curve here!  I appreciate your words.  

bob37 Posted at 2016-7-28 08:58
Thank you so much.  There sure is a learning curve here!  I appreciate your words.

As stated in the above post, you will most always lose video before RC control. You can expand the map and follow the line home and will regain video very quickly.

Greetings

Sir i have the same issue. My remote controller turns red still for how many seconds no sign of rth. Ive flown only 850 meters.