Negative values in a chart are not shown on Android App (and bad y-axis)

I did a DataFiled with VerticalSpeed, which can be positive and negative.

On Android the negative values are not visible, in the browser on the PC they are.

2. The formatting of the y-axis is also very bad. My values are rounded in steps of 50 (m/hours), the y-axis goes far to high myMax goes to 900 m/hour, but the axis is going till 2034!