After RTH activated, battery was 69% enough to come back 1.5 KM that spark travelled. It was strange that RTH was slow at 15 km/h (RC was in sports mode), also during the RTH it started rotating to the right. A slow speed resulted it to land 300m away from home point, it was a hassle to locate it later on. WHy slow speed of RTH and reason to trying to rotate on right side? I tried to cancel RTH to bring it fast but could not cancel even pressing cross many times. Pl. aee attached short video log.

RTH function disables Sport mode.  it will return at regular speed and this is dependant on wind speed.  as far a the shift to the right, id recommend you uploading your flight log to this post and have one of our inhouse gurus look at it.

I found log in mobile at \Phone\DJI\dji.go.v4\FlightRecord, it is attached.

Sparky_17 Posted at 2018-7-27 09:00
RTH function disables Sport mode.  it will return at regular speed and this is dependant on wind speed.  as far a the shift to the right, id recommend you uploading your flight log to this post and have one of our inhouse gurus look at it.

RTH is a "slow" sport, max speed 36-38 kph
But I go with the wind thing, must be heavily from the front and right, methinks

OP, please , upload it and link it
No need that lots of people upload it to phantom:

http://www.phantomhelp.com/logviewer/upload/

Hi. I am sorry for the trouble. Please contact DJI Support at support@dji.com for further analysis of your previous flight. Please sync the flight records as well using your DJI Go 4 application for further assessment on what happened to your previous flight with your DJI Spark.

Here is the link for the log.
http://www.phantomhelp.com/logviewer/Q3ZVMW7GLESKLMR76BGZ/

I have also send all details at support@dji.com

RTH speed is 22mph irregardless of what mode its in(sport vs Normal). Ac landed before homepoint because battery was in critical stage(only enough to safely land. You had high wind warnings , so thats probably why the lower airspeed on RTH, and yawing to right secondary to that wind as others have mentioned. Always fly into the wind on outleg of a flight so that the return journey doesnt have to fight the wind.

Tractable Posted at 2018-7-27 13:25
Here is the link for the log.
http://www.phantomhelp.com/logviewer/Q3ZVMW7GLESKLMR76BGZ/

You have some high wind warnings.

So the question is : how high was it in the air?

But the speed seems really a bit slow, too.

Hopefully the one or the other analysts will look into this topic

Considering wind was high up at height but how much was it? This is the question i have asked to DJI to answer from spark sensors. Spark gave occassional alarms only for high wind, means it was considered high on few occassions only. How Spark is calculating RTH speed, need to know that formulae to keep things clear in future. In my case spark not even once tried to return at high speed, it started very slow at 18 kph, why?
I myself make custom copters where i chose RTH speed myself, at high wind the current requirement of motor increased to some extent and there is a limit on throttle like 80%, thats it. So custom copter will try to maintain altitute, fight with air by increasing throttle and then return at that speed. I dont see such struggle from spark.

Have you been able to find your spark yet?  

Tractable Posted at 2018-7-28 04:36
Considering wind was high up at height but how much was it? This is the question i have asked to DJI to answer from spark sensors. Spark gave occassional alarms only for high wind, means it was considered high on few occassions only. How Spark is calculating RTH speed, need to know that formulae to keep things clear in future. In my case spark not even once tried to return at high speed, it started very slow at 18 kph, why?
I myself make custom copters where i chose RTH speed myself, at high wind the current requirement of motor increased to some extent and there is a limit on throttle like 80%, thats it. So custom copter will try to maintain altitute, fight with air by increasing throttle and then return at that speed. I dont see such struggle from spark.

I cannot recall the two speed levels of warnings
But one you can dismiss and it is a red square with white lettering.
The other is displayed in the place of the GPS green banner and cannot be dismissed.
It will display as long as the wind is high enough.

Using geocoding in your logs and Dark Sky weather, Your ground wind speeds were 7.17m/s but at your altitude of 200m, I am sure it was close to 25m/s up there.

So, as you went out on the trip you were flying with the wind.
But on the way back, you were fighting those 25m/s winds ergo the slower RTH speeds.

To prevent this in the future, drop the altitude and as mentioned before, fly into the wind on the way out.

pmshop Posted at 2018-7-30 05:49
I cannot recall the two speed levels of warnings
But one you can dismiss and it is a red square with white lettering.
The other is displayed in the place of the GPS green banner and cannot be dismissed.

ops, 25m/s? SPark RTH is ~10m/s, max speed is 14m/s
That would have given NO RTH at all, methinks
25mph, perhaps?

S-e-ven Posted at 2018-7-30 06:26
ops, 25m/s? SPark RTH is ~10m/s, max speed is 14m/s
That would have given NO RTH at all, methinks
25mph, perhaps?

You would be surprised up there
Maybe 25m/s gusts for sure

@Sparky_17, yes I found my spark using last location on map and the last frame of live video, it landed at a safe location. DJI should provide a way to continuously send pictures to the mobile when auto landing is activated, this will help to find spark later on.

@pmshop, i received occasional warnings of wind speed. Local weather that day was indicating 6-7 m/s, 25 m/s is i am sure not possible at 200m, decreasing altitude is good advice. If spark is measuring wind speed, it should indicate it on display.

I got reply from DJI help to calibrate IMU, i did and made two flights, RTH is now good at 33 km/h. If you change country, i recommend to calibrate both compass and IMU.

Tractable Posted at 2018-7-30 08:38
@Sparky_17, yes I found my spark using last location on map and the last frame of live video, it landed at a safe location. DJI should provide a way to continuously send pictures to the mobile when auto landing is activated, this will help to find spark later on.

@pmshop, i received occasional warnings of wind speed. Local weather that day was indicating 6-7 m/s, 25 m/s is i am sure not possible at 200m, decreasing altitude is good advice. If spark is measuring wind speed, it should indicate it on display.

", RTH is now good at 33 km/h"

just 33? Should be between 36 and 37/8ish!

Try a RTH with the wind from the back? ;-)