Don't know about ECO but definitely should work in Comfort. But i understand your "confusion" because i did encounter the same thing. Sometimes it looked like the car needs to be stopped in order to turn off StartStop, sometimes something else. Sometimes i wasn't even sure if it's not just about firm press
, so i gave it really solid push...
Anyway, try to press the button as far from you as possible (at the very border edge next to another button). Then it worked for me everytime until i coded it off completely.
