When for example we added a new business object which has a lower value, the lower value indicator is not updated and two indicators are shown.

The indicators and the markers are not updated when the data is changed at runtime.

Workaround:
Manually invalidate the arrange of the panel that holds the sparkline's markers. You can do that by finding the ScatterPanel control in the visual tree of the sparkline and then calling its InvalidateArrange() method. Call the InvalidateArrange() method at the moment when the data of the sparkline is updated. 

var panel = this.sparkline.FindChildByType<ScatterPanel>();
if (panel != null)
{
    panel.InvalidateArrange();
}

Indicators are not updated when new items are added runtime.