In addition, ExoPlayer.play (play button) is only triggered on every second attempt after clicking the stop button. And the sound (creek_3s.ogg, 3 sec) never stops until the stop button is pressed, regardless of whether the sound is looped or not.
… and by the way, if in my test app the switch for loop is set to off, the sound will not be lopped, but the sound will be restarted at the end. The difference to the loop is that it is not played gapless / seamlessly. The loop is seamless. So it is not a looping issue in my case.
If I loop a loop-able sound with the ExoPlayer, it will play seamlessly (without gaps).
If I play a loop-able sound with the ExoPlayer (ExoPlayer.Loop = false), the sound will play infinitely, but will not be looped (there will be a short gap at each repetition).
Ok, the second point will be fixed with the next release.
But what about the questions:
why ExoPlayer is always playing at Screen.Initialize and
why ExoPlayer.Stop does not work on Screen.Initialize. It can only be stopped by a timer (for whatever reason).