After being back to square 1, switching off after 30', I set the moment back to factory setting, configured it again and what a surprise, it worked again as expected. I set the idle timer back to 10min. in order to recognise the problem already after 10min instead of 30min. But the moment keeps playing now for more than an hour already. But I also noticed the software problems on BS Moment. It changes sometimes language, doesn't show the radio station or doesn't allow to change the radio station by using the display but only via app.
Hope the new release will solve those problems. I'm going to see the dealer tomorrow.