It seems that the Master Slide name is not retained when opening a presentation. The Aspose.Slides.MasterSlide.Name property is an empty string instead of the name specified when it is set in PowerPoint. I’ve attached a screenshot of my test and a reproducer project.
I have worked with source code shared by you using Aspose.Slides for .NET 16.8.0 and have been able to observe the issue. A ticket with ID SLIDESNET-37958has been added in our issue tracking system to resolve the issue. This thread has been associated with the ticket so that we share notification with you once issue will be fixed.