Thank you for contacting support.
We have worked with the data shared by you and have been able to reproduce the issue with below code snippet. A ticket with ID DIAGRAMNET-51672 has been logged in our issue management system for further investigation and resolution. The ticket ID has been linked with this thread so that you will receive notification as soon as the ticket is resolved.
// Call the diagram constructor to a VSDX diagram
Aspose.Diagram.Diagram diagram = new Aspose.Diagram.Diagram(dataDir + "Input_File.vsdx");
// Options when saving a diagram into Visio format
Aspose.Diagram.Saving.DiagramSaveOptions options = new Aspose.Diagram.Saving.DiagramSaveOptions(Aspose.Diagram.SaveFileFormat.VSDX);
diagram.Save(dataDir + "Output_File_19.7.vsdx", options);
We are sorry for the inconvenience.