Hi AIT MOUHOUB,
Diagram have support to copy/paste the nodes and connectors to another diagram. But, we are using serialization for copy and paste, and the below properties will not be serialized. So, these properties will be missing after paste into the diagram.
1. ShapeStyle of Node, Port and ConnectorGeometryStyle for Connector.(style properties in diagram)
2. ContentTemplate and Content.
To resolve or overcome this, please use create properties and maintain the same set of styles and keys(content template) for both diagrams.