As I don’t understand a single word of german, I am guessing only by your screenshot : the white line you are seeing is actually the snap point of an audio event.
It is used mainly to adjust the time position of an audio event differently from the use of the default start of it, when Snap is enabled.
It can be set (drag & drop) in the Sample editor : it is dispayed as a blue square labelled ‘S’ on the 0 - center line of the waveform.