I was flying my new Spark and the first 5 min of flight altitude seemed to be accurate but then I noticed that the altitude on my app went from 100 feet to zero.  I then tried to do a return home and it came back to my GPS home location but could not see it as it was lost in the fog (marine layer came rolling in fast).  The app said it was 0 altutude and to swipe to land but the app gave an audible warning that max altitude has been reached.   So I couldn't get drone to come down.  It finally desended due to battery level.  I later looked at the "Flight Record" portion of the Go 4 app and noticed that it never went lower than 100 feet and went all the way to 390 when at the home location.  I am assuming that because my return home altitude was set at 50m that it was trying to get the drone to 50m but couldn't because it was saying it was at 0.  So why did the app in the "Enter Device" mode get so confused?  This seems like an obviouse app error.  Is there a calibration that I need to do with the app itself to correct this?  I know that the barametric pressure probably caused the error but if the drone knew it's hight why did it not communicate that to the "Enter Device" part of the app?  This freaked me out so please help so that I don't have the same issue with a worse outcome.

It's not recommended to fly aircraft in the fog, the performance cannot be guaranteed.
Please fly it in a suitable environment, then check how it performs again, thanks.

Thank you Natalia.  I figured this out real quick.  I didn't start out in the fog.  Climate on the coast can change in seconds.  My question is why would it show on the live view when flying that it was at 0 altitude when I can look at the flight log/record and see what looks to be the accurate altitude reading of several hundred feet?  If something happens like this again how can I fix in the moment?  Can I go out of device and back in to reset?  I don't want to fly it into anything so is there a way to reset the app without losing contact with the drone when it's in the air to get an accurate altitude reading?  Or at least a different screen to help me understand what the drone is doing within Go 4?  Thank you for your help!

Did youe Spark got watered/soak/moist/dense due to fog?

DSanchez003 - No it did not show any signs of water damage.  I have flown several times since and no issues.  I still have no idea why I was getting conflicting altitude readings.  All I can say is that if you have issues with drastic fluctuations on your altitude bring it back without return home.  My RTH was set to 50m so app kept sending it higher and higher till it reached max height of 392 due to it thinking it was at 0.

Mine said I was at 120m when I was barley above 50m

could be a gps error, the vertical axis is the least accurate GPS calculation.  It might also use the downward facing sensor to estimate altitude under certain conditions, and i know for a fact that if you fly over something that is closer to the bottom than its minimum altitude it will climb, so maybe it was thinking it was close to the ground due to the fog and was climbing until it reached max flight altitude.  

TexasAerials Posted at 2017-8-2 13:34
could be a gps error, the vertical axis is the least accurate GPS calculation.  It might also use the downward facing sensor to estimate altitude under certain conditions, and i know for a fact that if you fly over something that is closer to the bottom than its minimum altitude it will climb, so maybe it was thinking it was close to the ground due to the fog and was climbing until it reached max flight altitude.

I get that but what I don't understand is why in "live" mode when flying it said 0 altitude but in the Flight Record it never said I was below 150 feet and all the way up to 400 feet?  Something is not communicating correctly to RC or app.

I believe it is ment to be Takeoff altitude. Go on a mountain above sea level and launch and have a fly. It will record your takeoff altitude above the sea level. I've done heaps of flying and I launch from sea level as I live on the beach. Mine still says 0 when everything else is accurate.