*edit, removed.

I was not able to reproduce it with our BackgroundBlur sample included in the plugin.
Is this only happening in your game or are you able to reproduce it in a separate simple project?

I could add a check before calling TransformToVisual to avoid the error message, but I want to understand why this is happening.

I think the error message is telling us that something is wrong, but I can't seem to figure out what the precise side-effect is to having a static singleton instance of my top-level UI, and how it is contributing to the behaviors I am seeing.

I have a very complex use-case for background blur effect, which involves two separate effects, and binding logic to tell a template which blur layer to use (to avoid cyclic dependencies).

[UIStateMachine]
<Controls>

[Root] (this is a static singleton)
[OverlayBlurSource]
[BackgroundBlurSource (Camera)]
[BaseLayer]
<BackgroundControlTitle>
-> BackgroundBlurSource

[OverlayLayer]
<TitleMenuControl>
<BackgroundEffect1>
-> OverlayBlurSource

• The first background blur source uses a 2D texture from the Unity camera. This is "Background Blur Source". Controls in the BaseLayer or OverlayLayer may reference this brush.
• The second background blur source combines everything in the "base" layer visual tree, including the original blur source. This is called "OverlayBlurSource". This is the blur source used by overlays.

I can see how referencing an incorrect layer causes a cyclic dependency. But what isn't clear is why it sometimes works, and sometimes doesn't, and always works in 3.2.1. As you suggest, it may be related to a different behavior / issue.

The warning message, " [NOESIS/E] Visuals don't have a common ancestor after domain reload." is now resolved by changing my binding approach.

Previously, binding BackgroundEffectBehavior.Source was accomplished as follows:

// code-behind:

public static readonly DependencyProperty BlurLayerProperty = DependencyProperty.Register("BlurLayer", typeof(FrameworkElement), typeof(BorderControlTitle), new PropertyMetadata(null));

public FrameworkElement BlurLayer
{
get { return (FrameworkElement)GetValue(BlurLayerProperty); }
set { SetValue(BlurLayerProperty, value); }
}

public override void OnApplyTemplate()
{
base.OnApplyTemplate();
if (Template != null && BlurLayer != null)
{
BackgroundEffectBehavior _BottomPanelBackgroundEffect = GetTemplateChild("_BottomPanelBackgroundEffect") as BackgroundEffectBehavior;
BackgroundEffectBehavior _TopPanelBackgroundEffect = GetTemplateChild("_TopPanelBackgroundEffect") as BackgroundEffectBehavior;

  if (_BottomPanelBackgroundEffect != null)
     _BottomPanelBackgroundEffect.Source = BlurLayer;
  if (_TopPanelBackgroundEffect != null)
     _TopPanelBackgroundEffect.Source = BlurLayer;

}
}

Binding is now accomplished as follows:

public static readonly DependencyProperty BlurLayerProperty = DependencyProperty.Register("BlurLayer", typeof(FrameworkElement), typeof(BorderControlTitle), new PropertyMetadata(null));

public FrameworkElement BlurLayer
{
get { return (FrameworkElement)GetValue(BlurLayerProperty); }
set { SetValue(BlurLayerProperty, value); }
}

// XAML:
<b:Interaction.Behaviors>
<noesis:BackgroundEffectBehavior Source="{Binding RelativeSource={RelativeSource AncestorType=local:BorderControlHero}, Path=BlurLayer}">
<BlurEffect Radius="{Binding Radius, Source={StaticResource BottomBlurRadius}}"/>
</noesis:BackgroundEffectBehavior>
</b:Interaction.Behaviors>

All error messages and crashes are now resolved.

Can this be closed then?

Yes. Thank you!