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();
}