When the values of the data points have great values and the axis has a very small manual range, the Path element does not render correctly and is at times not visible at all.

Workaround:
A possible way to resolve this is to use the Direct2DRenderOptions. The different render modes use a completely different rendering logic.
<telerik:LineSeries.RenderOptions>
 <telerik:Direct2DRenderOptions />
</telerik:LineSeries.RenderOptions>