UWP TextBox maximum lines limitation?

When I load four megabytes of text into TextBox only first 11300 lines are shown. The rest is blank. But even though it is blank I can still scroll trough it and can select text. When I paste it elsewhere text is present. It's just that the text doesn't show past 11300 lines. Is there some way to fix this problem?

Here is how it looks

Here is how i declare it in xaml:

   <RichEditBox 
            x:Name="ContentBox" 
            x:FieldModifier="public" 
            Grid.Row="0"
            KeyDown="Tb_KeyDown"
            GotFocus="Content_gotfocus"
            Loaded="Content_gotfocus"
            AcceptsReturn="True" 
            TextWrapping="NoWrap" 
            HorizontalAlignment="Stretch"
            VerticalAlignment="Stretch"
            IsSpellCheckEnabled="False"
            IsTextPredictionEnabled="False"
            TextReadingOrder="UseFlowDirection"
            FlowDirection="LeftToRight"
            TextAlignment="Left"
            >
        </RichEditBox>

OR

 <TextBox 
            x:Name="ContentBox" 
            x:FieldModifier="public" 
            Grid.Row="0"
            AcceptsReturn="True" 
            KeyDown="Tb_KeyDown"
            GotFocus="Content_gotfocus"
            HorizontalAlignment="Stretch"
            VerticalAlignment="Stretch"
            ScrollViewer.HorizontalScrollMode="Enabled"
            ScrollViewer.VerticalScrollMode="Enabled" 
            ScrollViewer.BringIntoViewOnFocusChange="True" 
            ScrollViewer.HorizontalScrollBarVisibility="Auto" 
            ScrollViewer.VerticalScrollBarVisibility="Auto" 
            TextWrapping="NoWrap" 
            IsSpellCheckEnabled="False"
            IsTextPredictionEnabled="False"
            Loaded="Content_gotfocus"

            TextReadingOrder="UseFlowDirection"
            FlowDirection="LeftToRight"
            TextAlignment="Left" LayoutUpdated="content_box_updated"
            />