in the bellow, example ignore Padding="{Binding Chart1Margin}" on the content view,  this is a holdover from other attempts to fix the issue and is not needed 

For anyone else who is struggling with this issue,

 

I have found a workaround, setting a height request on the chart resolves the issue, in my case I needed the chart to be sized dynamically by a grid layout.  I achieved this by nesting the chart in a content view and binding the chart's height request to the content view's Height. however, as the chart is a child of the content view we need a small buffer to parent layout cycling and infinite growth of the chart and content view. I set the chart's margin to -5 this lets the chart overflow the content view without resizing the content view; thus preventing infinite growth.

see the bellow code for an example

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"

<ContentView
    x:Name="CV1"
    Grid.Row="1"
    Grid.Column="1"
    Padding="{Binding Chart1Margin}"
    BackgroundColor="Transparent">
    <telerik:RadCartesianChart
        x:Name="Chart1"
        Margin="0,-5,0,-5"
        BackgroundColor="Transparent"
        HeightRequest="{Binding Source={x:Reference CV1}, Path=Height}">
        <telerik:RadCartesianChart.HorizontalAxis>
            <telerik:DateTimeContinuousAxis
                x:Name="AxisTime"
                LabelFontSize="{Binding TextSize}"
                LabelTextColor="{StaticResource CSTShadowColor}"
                LineColor="{StaticResource CSTShadowColor}"
                MajorStep="{Binding XAxisMajorStep}"
                MajorStepUnit="Second"
                Maximum="{Binding XAxisMax}"
                Minimum="{Binding XAxisMin}"
                PlotMode="OnTicks" />
        </telerik:RadCartesianChart.HorizontalAxis>
        <telerik:RadCartesianChart.VerticalAxis>
            <telerik:NumericalAxis
                x:Name="AxisY1"
                LabelFontSize="{Binding TextSize}"
                LabelTextColor="{StaticResource CSTShadowColor}"
                LineColor="{StaticResource CSTShadowColor}"
                Location="Left"
                MajorStep="{Binding Y1AxisMajorStep}"
                Maximum="{Binding Y1AxisMax}"
                Minimum="{Binding Y1AxisMin}"
                RangeExtendDirection="None"
                ShowLabels="True" />
        </telerik:RadCartesianChart.VerticalAxis>
        <telerik:RadCartesianChart.Series>
            <telerik:LineSeries
                CategoryBinding="Time"
                DisplayName="{Binding Y1AxisTitle}"
                ItemsSource="{Binding Data1}"
                Stroke="{StaticResource CSTSecondaryColor}"
                ValueBinding="Value" />
        </telerik:RadCartesianChart.Series>
        <telerik:RadCartesianChart.Grid>
            <telerik:CartesianChartGrid MajorLineColor="{StaticResource CSTShadowColor}" MajorLinesVisibility="X" />

        </telerik:RadCartesianChart.Grid>
    </telerik:RadCartesianChart>
</ContentView>

"

Hey is anything happening with this?