Inaccurate length and GPS lost depending on temperature

[EsTeeEmm]

Hi, maybe the 1001 post about this issue, I know. But I've recognized a curios thing about the measured length of my runs:

I'm running often the same track - in winter, spring summer etc. And the measuring depends on the temparature or weather conditions! In winter the track is 10-10.3km long when it becomes warmer the track starts growing 😉 then it becomes about 10.5km long!

I had this behaviour on my Gear S3 connected with S7 Edge, Apple Watch 3 with iPhone 8 and now on my Ionic with iPhone 8! A frient with Apple Watch and Runtastic says the same. What happend here?

And, about the gps losses of my Ionic: Thru the cold winter and no leaves on the trees I had no problems with gps lost. But now, as the forest becomes deeper with the leaves etc. the losses grow!

But only on the Ionic, my iPhone has no problems! The mad thing: Last week was very cold but I had no losses of GPS!  I always wait to "connect before I start the run! 

Moderator edit: Updated subject for clarity 

[SilviaFitbit]

A warm welcome to the Community @EsTeeEmm. I appreciate the time that you took to share these details in the forums. 

Fitbit Ionic has built-in GPS. When you select a GPS exercise, Ionic vibrates when it finds a GPS signal. Environmental factors including tall buildings, dense forest, steep hills, and even thick cloud cover can interfere with your watch's ability to connect to GPS satellites. 

At least 24 GPS satellites are constantly in orbit around the Earth and broadcasting data. All GPS devices, whether your phone or a Fitbit device, require a direct path to these satellites in order to receive their radio transmissions. If the signal is blocked—either because you're underground, near many tall buildings, or as a result of atmospheric effects—GPS won't work. While GPS gives you a more accurate measure of distance than step counting alone, the actual accuracy depends on both your environment and the weather.

I'll be around if you need further assistance.