I have found the problem. It was my mistake, I've added series twice like
NGridSurfaceSeries surface = (NGridSurfaceSeries)nChartDin.Charts[7].Series.Add(SeriesType.GridSurface);
and after all manipulations
nChartDin.Charts[7].Series.Add(surface);

But why one of the series was empty?

In general a series is not supposed to be added twice to a chart (or added to different charts).
In the following code the second Add method throws an ArgumentException with message "The specified element is already added to the document".

NGridSurfaceSeries series = (NGridSurfaceSeries)chart.Series.Add(SeriesType.GridSurface);
chart.Series.Add(series);

It is strange that you've managed to add the same series to a chart two times.

Best Regards,
Nevron Support Team

I remember this exception, I've got such when worked with line series.
Maybe this happened because I've added serie first, then changed its settings and then tried to add again? And in that case exception doesn't throw?