Yesterday I rode for 3h with my Charger 8m (on the snow), I've used it for the second time and I am starting to understand how it has to be flight, the first approach is not easy because of the amazing turning speed of the kite but once you can control it, you will love it.
I noticed that it loses power when I pull the bar, it seems it loves to be driven like an old C-kite (not to much pressure on the Bar), doesn't it?
The second thing I noticed is that the kite tends to fall behind in the center of the window in case of few wind or when I pull the bar too much (like a SLE pump kite), is it normal or am I doing something wrong?

From what you've described the wind is too light and you're tail stalling the kite IMO.

What is the windspeed you're flying it in?

it was between 11-14 knots

Sounds like you were right around the bottom end of it's wind range.

Not that it will change things a lot but running your back strap loose may help a bit ?

2nd Bladerunner. The 8m is a sweet high wind kite and you were definitely in the lower end of the range.

today I run the CH 8m with 16-20knots, no stall, no problem, Amazing turnspeed, I am a little bit scared when I jump because it's too fast and in a hurry it loops.

I did my 1st kite loop completely by accident when I was running my 15m Charger. I didn't even realise I did it until I saw the twist in my lines.

The 8m Loops like a fiend and builds a ton of power in the process. A lot of people were scared off by the 8m's speed and sensitivity but if you take the time to get a fell she's a riot to fly.