If the cell phone disconnects from the control wifi during the flight, the drone lost signal with the control!
I will explain what happened and ask your engineers to analyze to see if this is not the problem:

I identified a serious problem in the spark that has happened to me twice: On both occasions I was in a place where the wifi of the residence has internet and my cell phone has access. I was using Android 7 on the S7 Edge, once with DJI last version (ending 18) and another with the previous (ending 15). What happens is the following:
I connect the cell phone to the wifi control, I go into the application and I take the takeoff with the drone and I fly around 15 or 20m distance and height, then after a few minutes I get in control and I see that the drone does not respond. I look at the indicator light on control and note that it is red, ie the control is not connected to the drone.
Then I look at the wifi and I see that my cell phone has connected to the wifi in my house, however I have disabled the "smart network exchange" of the android.
In both times I panic because as the drone is next, it does not execute the RTH and begins to land. The first time he landed on the neighbor's roof (I had to use a ladder and ask permission) and the second time he landed in the middle of the bush.
I could not avoid the landing because the control did not respond. I turned the control off and then reestablished the signal the drone had already landed.
From what I understand, this happened exactly: my cell phone disconnected from the control wifi, however instead of the spark obeying the control, some interference broke the connection between the control and the spark.

Since DJI does not consider official support for the OTG cable (as commented earlier in https://forum.dji.com/thread-122902-1-1.html), I would like to know how we are since using Wi-Fi I do not have more security and no confidence in flying, unless I buy a new phone and let him just fly with the spark

First it’s best to fly in airplane mode no Bluetooth turned on the less interference the better, so shut down cell WiFi and just use RC WiFi from phone to remote.

Second your aircraft is landing because it is within 20 metres of homepoint and you need to change this in your settings for RTH , so go to your RTH settings while your Aircraft is turned on and change the setting for within 20 metres to RTH , your Aircraft will RTH at its present height if higher than 2.5metre if lower than 2.5 metre then it will ascend to 2.5 metre and RTH and land at homepoint.

It's explained in detail on pages 13 and following in the user manual: https://www.dji.com/spark/info#downloads

hallmark007 Posted at 2017-12-8 05:25
First it’s best to fly in airplane mode no Bluetooth turned on the less interference the better, so shut down cell WiFi and just use RC WiFi from phone to remote.

Second your aircraft is landing because it is within 20 metres of homepoint and you need to change this in your settings for RTH , so go to your RTH settings while your Aircraft is turned on and change the setting for within 20 metres to RTH , your Aircraft will RTH at its present height if higher than 2.5metre if lower than 2.5 metre then it will ascend to 2.5 metre and RTH and land at homepoint.

please explain me better what you mean by: "so shut down cell WiFi and just use RC WiFi from phone to remote."
I put my phone in airplane mode, I turn off the bluethooth, wifi and 3g. So I only enable the wifi.
However as I am in front of my house I have on my wifi the networks of my house and the network of the drone. I connect in the drone's net and go out to fly.
This is the procedure I always do, however, without my desire, the cell phone disconnects itself from the wifi network of the control and connects to the network of my house. And when this happens the control loses the signal with the drone as well.
So the solution would be for me to delete all the saved networks on my cell phone? If so, then I will have to leave a cell phone exclusively to fly with the drone and not use in anything else

Wachtberger Posted at 2017-12-8 05:39
It's explained in detail on pages 13 and following in the user manual: https://www.dji.com/spark/info#downloads

I already imagined this. The most serious problem I consider is the loss of the connection from the control to the drone because of the reason for the cell and the control to lose the connection.

ZmaroSobrinho Posted at 2017-12-8 09:36
please explain me better what you mean by: "so shut down cell WiFi and just use RC WiFi from phone to remote."
I put my phone in airplane mode, I turn off the bluethooth, wifi and 3g. So I only enable the wifi.
However as I am in front of my house I have on my wifi the networks of my house and the network of the drone. I connect in the drone's net and go out to fly.

If you have your phone in airplane mode it should not connect to your house WiFi , this is strange , have you tried to use forget about house WiFi into your phone just to try to see if this helps, or how is it working when you are out of range of House WiFi ?

hallmark007 Posted at 2017-12-8 09:46
If you have your phone in airplane mode it should not connect to your house WiFi , this is strange , have you tried to use forget about house WiFi into your phone just to try to see if this helps, or how is it working when you are out of range of House WiFi ?

so I understand this is a problem in 2 parts: The first is the android that disconnects from the control and connects at home. The second and most dangerous is the wifi of the cellular disconnect in the control and the control lose the signal with the drone. This should not happen. If I am flying with it far away and my cell phone runs out, will the drone lose radio signal with the control?
before I had a standard phantom 3 and this did not happen. If the cell phone hung up I could quietly keep the control

ZmaroSobrinho Posted at 2017-12-8 10:11
so I understand this is a problem in 2 parts: The first is the android that disconnects from the control and connects at home. The second and most dangerous is the wifi of the cellular disconnect in the control and the control lose the signal with the drone. This should not happen. If I am flying with it far away and my cell phone runs out, will the drone lose radio signal with the control?
before I had a standard phantom 3 and this did not happen. If the cell phone hung up I could quietly keep the control

If you lose your app or app crashes you would still have control, if you lose radio control for more than 3 seconds your Aircraft will RTH.

The only WiFi connection you need is private WiFi from phone to RC, for get home WiFi forget cell WiFi .

You should really test away from any other WiFi then you will know that your problem is not with RC WiFi or it is, but I don’t think it will.

Everything works the same as in phantom or Mavic except for spark uses WiFi between RC and phone, not cable at this moment in Time.

You could always try OTG with very 4.1.15 or earlier, this is what a lot of people are doing.

Until DJI adds support for otg in newer software versions. iOS currently works with otg with iOS 11.2 and DJI go 4.1.18.

ZmaroSobrinho Posted at 2017-12-8 09:40
I already imagined this. The most serious problem I consider is the loss of the connection from the control to the drone because of the reason for the cell and the control to lose the connection.

Hi, sir. Did you put your antenna in the right position? I would recommend you enter wifi setting and see if most the channels are green. Please try to fly in a wide place without interference.

I seem to be missing something here. When I put my iPhone in airplane mode, WiFi and Bluetooth will disable. So with no WiFi, how is the phone connecting to RC?

JJ Wright Posted at 2018-1-26 19:28
I seem to be missing something here. When I put my iPhone in airplane mode, WiFi and Bluetooth will disable. So with no WiFi, how is the phone connecting to RC?

i put in airplane mode and later i turn on just wifi on phone

I have the same issues yesterday did nothing different started dji spark then controller and phone wifi connection and OTG plug in the controller. Lost contact and it landed as should. However love some tips on a better secure connection etc.

On son's ipad air not as bad but regardless need better update to make better. In saying that generally wifi on devices are very poor upto 14-20 metres max as I've been informed by a few techs.

Just poor range and strength but that's a downside in a modern world with wifi devices everywhere and not to forget mental objects etc.

The dji go v4 does have another issue the flight data zone doesn't update via wifi or cellular internet connection. Nor does it work on macbook air which is a shame in the current version

Hopefully to get a better update soon for better flying and control.

ZmaroSobrinho Posted at 2017-12-8 10:11
so I understand this is a problem in 2 parts: The first is the android that disconnects from the control and connects at home. The second and most dangerous is the wifi of the cellular disconnect in the control and the control lose the signal with the drone. This should not happen. If I am flying with it far away and my cell phone runs out, will the drone lose radio signal with the control?
before I had a standard phantom 3 and this did not happen. If the cell phone hung up I could quietly keep the control

Maybe your cell phone connect to your house network because it was first disconnected from the spark network, maybe not the other way around.

It happened to me the same thing, my phone disconnected and the RC disconnected at the same time. I think the interference that made the phone disconnect also affected the RC and made it disconnect. My Spark was farther from its home point so it suddenly rise to 90 meter and started coming home. Then it reconnected to the RC but the phone never reconnected and I landed the drone without the phone.

One thing you could do is to unplug your router temporary while you fly the Spark and then plug it back when you're done flying. See if that help.

In my situation, I think I did something wrong by having the drone nearly over me with the antennas pointing right at it or almost at it, not the correct orientation.