This is a regressiion issue in the 2024.3.924 release of Telerik UI for WPF.
Save and load of the saved XML should result of the same item IDs for every RadDiagramItem (shapes, connections).

To work this around, you can create a custom SerializationService and override its DeserializeItems method, where you can change the "makeUnique" parameter.

The issue manifests also when doing drag/drop from the RadDiagramToolBox or any other custom drag drop implementation that uses the DiagramDropInfo class (which is automatically handled by the RadDiagram's drop internal code). In this case the custom service approach won't work because the drag/drop deserialization works with a separate instance of SerializationService (SerializationService.Default) which cannot be changed. In this case, you can subscribe RadDiagram to the DragDropManaged.Drop event and manually call the SerializationService.Default.DeserializeItems method.

 public class CustomSerializationService : SerializationService
 {
     public CustomSerializationService(IGraphInternal graph) : base(graph)
     {
     }

     public override IEnumerable<IDiagramItem> DeserializeItems(SerializationInfo serializationInfo, bool makeUnique = false)
     {
         makeUnique = false;
         return base.DeserializeItems(serializationInfo, makeUnique);
     }
 }

 public MainWindow()
 {
     InitializeComponent();

     this.diagram.ServiceLocator.Register<ISerializationService>(new CustomSerializationService(this.diagram));

     DragDropManager.AddDropHandler(this.diagram, OnDiagramDrop);
 }

 private void OnDiagramDrop(object sender, Telerik.Windows.DragDrop.DragEventArgs e)
 {
     var data = DragDropPayloadManager.GetDataFromObject(e.Data, typeof(DiagramDropInfo).Name);
     if (data is DiagramDropInfo)
     {
         SerializationService.Default.DeserializeItems(((DiagramDropInfo)data).Info, false);
     }
 }

In the Swimlane diagram example (Data Visualization -> Diagrams -> Swimlane) the application crashes, showing at least one but often more than one error message.

How to reproduce:

• Open the Swimlane example.
• Click the area that is labelled as "Process name" (also marked in the attached screenshot)
• One or multiple Message boxes containing the exception message

{DependencyProperty.UnsetValue} is not a valid value for the Property "Background"

pop up (see other screenshot)

NullReferenceException is thrown when trying to save RadDiagram instance that contains a RadDiagramShape with its Geometry assigned to a GeometryGroup value. 

To work this around, you can flatten the GeometryGroup before setting the shape's Geometry property. This is done by calling the GetFlattenedPathGeometry() method of the GeometryGroup.

shape.Geometry = group.GetFlattenedPathGeometry();

Most problematic issue when container can contains a container inside of it.

In mvvm demo project i modified load/save button to Clear diagram and display different content.

It works but after few click there is a recurrence call to update Z indices.

The reason to create such combination is to have hierarchy in diagram to display diagram from general view to detailed view.

Currently, the content of RadDiagramShape element alignment can be changed via its HorizontalContentAlignment and VerticalContentAlignment. However, in RadDiagramTextShape, those properties don't take effect. Instead the text content is always centered.

At this point, you can achieve this requirement, by extracting the ControlTemplate of RadDiagramTextShape and bind the corresponding properties of the ContentPresenter to the parent shape. For example:

<ContentPresenter x:Name="NormalContent"
				  Margin="{TemplateBinding Padding}"
				  HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
				  VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>

In a NetCore project, when dragging the diagram from the toolbox into the designer, an exception is thrown inside the designer. 

With Visual Studio 2019 Preview v. 16.10.0. Preview 2.0, Net 5 project => when dragging from the ToolBox - the VS goes into a non-responsive state (Vs is busy is shown or the VS crashed and closed automatically).

StackOverflowException is thrown when the Layout() method of RadDiagram is called and the diagram's router is OrgTreeRouter. To reproduce this  use TreeLayoutSettings.

To work this around, add bigger HorizontalSeparation and VerticalSeparation for the TreeLayoutSettings. Or disable the connections routing using the RouteConnections property of RadDiagram.

The exception throws when you use RadDiagram in a data binding scenario by populating its GraphSource and you want to draw a shape using the RadDiagramRibbon's ShapeTool. 

InvalidOperationException: 'Cannot modify the Items collection when the GraphSource is set.'

To work this around, use the PreviewMouseDown, PreviewMouseMove and PreviewMouseUp events of RadDiagram in order to prevent the default logic executed by the ShapeTool. Then, in the event handlers, implement a custom logic that works with the diagram GraphSource.

private void RadDiagramRibbon_Loaded(object sender, RoutedEventArgs e)
{
	var toolService = diagram.ServiceLocator.GetService<IToolService>() as ToolService;
	this.shapeTool = (ShapeTool)toolService.ToolList.FirstOrDefault(x => x is ShapeTool);
}

private Point startPoint;
private bool isShapeCreationInProgress;
private MyNode currentShapeModel; // where MyNode derives from NodeViewModelBase and expose an additional Geometry property 
private ShapeTool shapeTool;

private void RadDiagram_PreviewMouseDown(object sender, MouseButtonEventArgs e)
{			
	if (this.shapeTool.IsActive && !this.isShapeCreationInProgress)
	{
		this.isShapeCreationInProgress = true;
		this.startPoint = this.diagram.GetTransformedPoint(e.GetPosition(this.diagram));

		this.currentShapeModel = new MyNode()
		{
			Geometry = this.shapeTool.Geometry,
			Position = this.startPoint,
			Width = 0,
			Height = 0
		};
		var source = (MyGraphSource)this.diagram.GraphSource;
		source.AddNode(this.currentShapeModel);
		e.Handled = true;
	}
}

private void RadDiagram_PreviewMouseMove(object sender, MouseEventArgs e)
{
	if (this.shapeTool.IsActive && this.currentShapeModel != null && this.isShapeCreationInProgress)
	{
		var transformedPoint = this.diagram.GetTransformedPoint(e.GetPosition(this.diagram));
		var width = Math.Abs(this.startPoint.X - transformedPoint.X);
		var height = Math.Abs(this.startPoint.Y - transformedPoint.Y);
		var x = Math.Min(this.startPoint.X, transformedPoint.X);
		var y = Math.Min(this.startPoint.Y, transformedPoint.Y);

		this.currentShapeModel.Width = width;
		this.currentShapeModel.Height = height;
		this.currentShapeModel.Position = new Point(x, y);
		e.Handled = true;
	}
}

private void RadDiagram_PreviewMouseUp(object sender, MouseButtonEventArgs e)
{
	this.isShapeCreationInProgress = false;
	e.Handled = true;
}

While performing Cut operation inside RadDiagram, an exception in the MS Clipboard occurs with the following message:

System.Runtime.InteropServices.COMException: 'OpenClipboard Failed (Exception from HRESULT: 0x800401D0 (CLIPBRD_E_CANT_OPEN))'