Unfortunately today I've encountered a problem again, in a version of my application where I've implemented the "fix". Again the error only happens sometimes. Usually simply reloading the webpage fixes the issue.
<Border Margin="2,2,8,2" Grid.Column="0" Background="#33000000" >
<Border.Resources>
<Style x:Key="CustomAxis" TargetType="chartview:Axis">
<Setter Property="LabelStyle">
<Setter.Value>
<Style TargetType="TextBlock">
<Setter Property="Margin" Value="1"/>
<Setter Property="Foreground" Value="White" />
</Style>
</Setter.Value>
</Setter>
<Setter Property="MajorTickStyle">
<Setter.Value>
<Style TargetType="Rectangle">
<Setter Property="Fill" Value="#FFD7D7D7"/>
<Setter Property="Opacity" Value="0.3"/>
</Style>
</Setter.Value>
</Setter>
</Style>
</Border.Resources>
<radchartview:RadCartesianChart x:Name="ChartJam"
MouseWheel="ChartJam_MouseWheel"
MouseLeftButtonUp="ChartJam_MouseLeftButton"
Loaded="ChartJam_Loaded"
Height="Auto" MinHeight="100"
Width="Auto" MinWidth="200"
>
<radchartview:RadCartesianChart.VerticalAxis>
<chartview:LinearAxis Title="" Style="{StaticResource CustomAxis}"
/>
</radchartview:RadCartesianChart.VerticalAxis>
<radchartview:RadCartesianChart.HorizontalAxis>
<chartview:DateTimeContinuousAxis
PlotMode="OnTicks" Style="{StaticResource CustomAxis}"
MajorStepUnit="{Binding MajorStepUnit}"
MajorStep="{Binding MajorStep}"
LabelFormat="{Binding LabelFormat}"
Minimum="{Binding MinimumDateTime}"
LabelFitMode="Rotate"
Title=""
/>
</radchartview:RadCartesianChart.HorizontalAxis>
<radchartview:RadCartesianChart.Behaviors>
<chartview:ChartPanAndZoomBehavior ZoomMode="None"
PanMode="None"/>
<chartview:ChartTrackBallBehavior ShowIntersectionPoints="True"
ShowTrackInfo="True"
SnapMode="ClosestPoint" />
</radchartview:RadCartesianChart.Behaviors>
<chartview:AreaSeries ItemsSource="{Binding LineData}"
CategoryBinding="DtJamLength"
ValueBinding="JamLength"
StrokeThickness="1"
Stroke="#FF93D427"
Fill="#AA93D427"
>
<chartview:AreaSeries.TrackBallInfoTemplate>
<DataTemplate>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="Auto" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<TextBlock Grid.Row="0" Grid.ColumnSpan="2" FontWeight="Bold" HorizontalAlignment="Center"
Text="{Binding Labels.ChartLast24Hours, Source={StaticResource PublicLabels}}" />
<TextBlock Grid.Row="1" Grid.Column="0" FontWeight="Bold"
Text="{Binding Labels.Timestamp, Source={StaticResource PublicLabels}, Converter={StaticResource StringToLabelConverter}}" />
<TextBlock Grid.Row="1" Grid.Column="1"
Text="{Binding DataPoint.Category, StringFormat='dd/MM/yyyy HH:mm'}" />
<TextBlock Grid.Row="2" Grid.Column="0" FontWeight="Bold"
Text="{Binding Labels.JamLength, Source={StaticResource PublicLabels}, Converter={StaticResource StringToLabelConverter}}" />
<TextBlock Grid.Row="2" Grid.Column="1"
Text="{Binding DataPoint.Value,StringFormat=\{0:n2\}km}" />
</Grid>
</DataTemplate>
</chartview:AreaSeries.TrackBallInfoTemplate>
</chartview:AreaSeries>
<radchartview:RadCartesianChart.Grid>
<chartview:CartesianChartGrid MajorLinesVisibility="XY" IsTabStop="False">
<chartview:CartesianChartGrid.YStripeBrushes>
<SolidColorBrush Color="Pink" Opacity="0.9" />
<SolidColorBrush Color="Transparent" />
</chartview:CartesianChartGrid.YStripeBrushes>
<chartview:CartesianChartGrid.XStripeBrushes>
<SolidColorBrush Color="#FFD7D7D7" Opacity="0.3" />
<SolidColorBrush Color="Transparent" />
</chartview:CartesianChartGrid.XStripeBrushes>
</chartview:CartesianChartGrid>
</radchartview:RadCartesianChart.Grid>
</radchartview:RadCartesianChart>
</Border>