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Slow User Control Loading WPF: ListBox doesn't virtualize

My MVVM WPF application uses Linq2SQL for using SQL Server Express. I noticed after populating the database with real data I get some big delays for the UI to update and thought is was my query/ grouping strategy. But, while some of the data fills take more than 100ms, rarely do they take more than 200ms but I'm seeing a lag of up to 3 seconds on the window refresh. EDIT FOR BREVITY:
I was wrapping my ItemsControl in a ScrollViewer:
<ScrollViewer VerticalScrollBarVisibility="Auto" Grid.Column="0" Grid.Row="3" Grid.ColumnSpan="2" ScrollChanged="ScrollViewer_ScrollChanged">
<ItemsControl x:Name="DivisionItems" ItemsSource="{Binding oObsByDiv}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<uc:ucObservationsHeader/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</ScrollViewer>
But after some hints from below and reading up on Virtualization I now use a ListBox like so:
<ListBox x:Name="DivisionItems" Grid.Column="0" Grid.Row="3" Grid.ColumnSpan="2"
ItemsSource="{Binding oObsByDiv}"
ScrollViewer.CanContentScroll="True"
VirtualizingStackPanel.ScrollUnit="Pixel">
<ListBox.Template>
<ControlTemplate>
<ScrollViewer VirtualizingStackPanel.IsVirtualizing="True"
VirtualizingStackPanel.VirtualizationMode="Recycling">
<ItemsPresenter/>
</ScrollViewer>
</ControlTemplate>
</ListBox.Template>
<ListBox.ItemsPanel>
<ItemsPanelTemplate>
<VirtualizingStackPanel/>
</ItemsPanelTemplate>
</ListBox.ItemsPanel>
<ListBox.ItemTemplate>
<DataTemplate>
<uc:ucObservationsHeader/>
</DataTemplate>
</ListBox.ItemTemplate>
The user control used for the Items in that template then calls another user control that I'm wrapping in another ListBox in a very similar manner:
<ListBox ItemsSource="{Binding lObs}" Grid.Row="1" Grid.Column="1"
HorizontalContentAlignment="Stretch" ScrollViewer.HorizontalScrollBarVisibility="Disabled"
ScrollViewer.CanContentScroll="True"
VirtualizingStackPanel.ScrollUnit="Pixel">
<ListBox.Template>
<ControlTemplate>
<ScrollViewer VirtualizingStackPanel.IsVirtualizing="True"
VirtualizingStackPanel.VirtualizationMode="Recycling">
<ItemsPresenter/>
</ScrollViewer>
</ControlTemplate>
</ListBox.Template>
<ListBox.ItemsPanel>
<ItemsPanelTemplate>
<VirtualizingStackPanel/>
</ItemsPanelTemplate>
</ListBox.ItemsPanel>
<ListBox.ItemTemplate>
<DataTemplate>
<uc:ucObservationsView/>
</DataTemplate>
</ListBox.ItemTemplate>
But the multiple second lag still exists. The outer user control is instantiated 15 times, and the inner one has on average 15 items each. What is it that is breaking virtualization in this case? I keep stripping out the ScrollUnit and CanContentScroll in one or both places, as well as the HorizontalContentAlignement and the HorizontalScrollBar visibility, but those just affect the look without seeming to be the cause for breaking virtualization.

Nested ItemsControls optimizations

I have a question regarding nested collections usage in UWP apps with XAML/C#.
Let's say I have a list of items with multiple images in each.
I need to show a scrollable list with all of the images inside the item data.
So far I can see a solution to create GridView with ItemsTemplate that has ItemsControl inside it. But it seams very slow and not optimized solution.
Is there any better suggestion to solve that?

Without much context, I can only think of following :
You have a large amount of data to be displayed, but not all at once. In this case you should consider using controls that support virtualization.
Flattening the data source before binding it. This may improve the performance by a little.
Update
Here is how you can do it :
<ListViewItem ItemsSource="{Binding Posts}">
<ListView.ItemsPanel>
<ItemsPanelTemplate>
<VirtualizingStackPanel />
</ItemsPanelTemplate>
</ListView.ItemsPanel>
<ListView.ItemTemplate>
<DataTemplate>
<StackPanel>
<TextBlock Text="{Binding Title}" />
<TextBlock Text="{Binding Message}" />
<ScrollViewer HorizontalScrollBarVisibility="Auto">
<ItemsControl ItemsSource="{Binding Photos}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<VirtualizingStackPanel />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<Image Source="{Binding}" />
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</ScrollViewer>
</StackPanel>
</DataTemplate>
</ListView.ItemTemplate>
</ListViewItem>

many webview inside flipview winrt

I have flipview and inside flipview there is a webview. But I have a problem. If I binding too many items on this flipview my flipview get crashed. This is the xaml from my flipview
<FlipView Grid.Column="1" Grid.RowSpan="2" HorizontalAlignment="Center" HorizontalContentAlignment="Center"
x:Name="BookPageContentFlipView" Tapped="OnBookPageContentFlipViewTapped"
DoubleTapped="OnBookPageContentFlipViewDoubleTapped"
ItemsSource={Binding BookPages} SelectionChanged="BookPageContentFlipViewSelectionChanged">
<FlipView.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Horizontal" />
</ItemsPanelTemplate>
</FlipView.ItemsPanel>
<FlipView.ItemTemplate>
<DataTemplate>
<Grid>
<Webview Source={Binding Book}/>
</Grid>
</DataTemplate>
</FlipView.ItemTemplate>
</FlipView>
It just a sample but actually I load from local string. So how do I can bind many items to this flipview?

WPF/MVVM Wrap panel orientation

I'd like to display basically a matrix of buttons, the number of buttons change in runtime.
My problem is that I want them to be next to each other to fill up all the space I give them. I thought WrapPanel is the perfect way to do that but it puts the buttons under each other and I have no idea how to solve it.
<Grid>
<WrapPanel Width="250" Height="50" Orientation="Horizontal" Margin="543,442,73,162" >
<ItemsControl ItemsSource="{Binding States}" >
<ItemsControl.ItemTemplate>
<DataTemplate >
<Button Width="50" Height="25" Content="{Binding StateName}" Padding="0" ></Button>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</WrapPanel>...</Grid>
States is a list of Items that contains a name and a ID number. If i want to add or remove buttons I modify the list. So the buttons appear but in vertical order and they go beyond the limits of the WrapPanel so if it is not big enough only some appears. They only use 50 width from the 250 and more then the 50 height. In this case if I put 5 buttons in it only shows 2 of them.

Don't wrap ItemsControl inside WrapPanel. Instead set it as ItemsPanel of ItemsControl.
<ItemsControl ItemsSource="{Binding States}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<Button Width="50" Height="25" Content="{Binding StateName}"
Padding="0"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<WrapPanel/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
</ItemsControl>

Windows Store App ListView: How to use the GroupStyle?

am porting a Windows Phone App to Windows Store and trying to create a grouped ListView. There is a good article in the Dev Center and grouping the list is no problem. But there are some things I do not understand about the GroupStyle.
The example from the article uses a GroupStyleSelector that leads to the following GroupStyle:
<GroupStyle x:Key="listViewGroupStyle">
<GroupStyle.HeaderTemplate>
<DataTemplate>
<Grid Background="LightGray" >
<TextBlock Text='{Binding Key}' Foreground="Black" Margin="10"
Style="{StaticResource SubheaderTextBlockStyle}" />
</Grid>
</DataTemplate>
</GroupStyle.HeaderTemplate>
<GroupStyle.Panel>
<ItemsPanelTemplate>
<VariableSizedWrapGrid MaximumRowsOrColumns="3" Orientation="Horizontal"/>
</ItemsPanelTemplate>
</GroupStyle.Panel>
</GroupStyle>
The purpose of GroupStyle.HeaderTemplate is obvious and changes on this template can be directly observed in the running app.
But what is GroupStyle.Panel good for? The docs says:
Gets or sets a template that creates the panel used to lay out the items.
Ok, but no matter how I change ItemsPanelTemplate (BackgroundColor, Orientation, etc.), the List does not change in the running app.
Additionally there is GroupStyle.ContainerStyle which is not used in the Example. If add this to the GroupStyle this has no influece on the list in the running app as well.
So, what are GroupStyle.Panel and GroupStyle.ContainerStyle good for? How are the used correctly?

I found out that you need to set the ItemsPanel of the ListView, too. By default the ItemsStackPanel is used and that doesn't seem to allow any custom panel in a grouped ListView. When setting the ItemsPanel to a VirtualizingStackPanel, the custom panel is applied, BUT the headers are not sticky anymore. It seems that there is something broken about the current ListView/ItemsStackPanel implementation and as we do not have source access it's hard to tell what.
<ListView
ItemsSource="{Binding Source={StaticResource namesSource}}"
>
<ListView.GroupStyle>
<GroupStyle>
<GroupStyle.HeaderTemplate>
<DataTemplate>
<TextBlock Text="{Binding Key}" Foreground="Yellow" FontSize="{ThemeResource HubHeaderFontSize}" Margin="6" />
</DataTemplate>
</GroupStyle.HeaderTemplate>
<GroupStyle.Panel>
<ItemsPanelTemplate>
<controls:WrapPanel />
</ItemsPanelTemplate>
</GroupStyle.Panel>
</GroupStyle>
</ListView.GroupStyle>
<ListView.ItemsPanel>
<ItemsPanelTemplate>
<!--<ItemsWrapGrid FlowDirection="LeftToRight" Orientation="Vertical"/>-->
<VirtualizingStackPanel Orientation="Vertical"/>
<!--<ItemsStackPanel Orientation="Vertical"/>-->
</ItemsPanelTemplate>
</ListView.ItemsPanel>
<ListView.ItemTemplate>
<DataTemplate>
<Grid Background="AliceBlue" Margin="3,0">
<TextBlock Text="{Binding}" Foreground="Black" Margin="4,2"/>
</Grid>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>