"LiveTrack Ended" always in 10-15 seconds after I start my activity

what do you mean with "recipient picked on the watch". I set the email adress of the recepients in Connect on my phone. And with turning the LiveTrack on, I select "E-mail". After pressing start running, the email is send and LiveTrack is on during total activity. Is it possible your phone looses connection to 4g?

by "recipient picked on the watch" I mean that I have at least one recipient selected who will receive emails.

There is no chance I constantly loose connection to 4G right at the time of running. While on the phone never had any hiccup when connection is concerned so 0% chance that right 10-15 seconds of my every run connection is lost

put an e-mail of the one, who should get the link in Connect app. Then on the watch you should have in the Livetrack settings => e-mail: on, recipient: 1

yup that's what I have been doing. All this is correctly set up on my watch prior to starting my workout and in 10-15 seconds after the start I get a prompt "LiveTrack Ended"

Ok, so check the connection between watch and phone. Meaning - maybe connect app is killed quickly due to the "battery optimization' function? 
As long you have mobile data available, and the app is not going in to the deep sleep due to the phone setting - it always work. Tested with many watches & phones in last 5 years, as I use this almost every day ;) 

you can also try to do the following:

- start an activity

- wait, until you'll get an info, that Livetrack was ended

- grab a phone and open Connect app

if this is the phone, which is killing the connection, you'll have the answer by getting an info, that Livetrack was resumed.

how shall I know if the phone is killing it?

I am at the balcony, phone in my hand, Connect app turned on. Getting GPS, LiveTrack ready sign on my watch, start the activity. In 10-15 seconds "LiveTrack Ended" while I see on my phone connection is on.

do you run iOS or Android?

iOS and never had connection issues between my phone and watch