Thanks for inquiring Aspose.Slides.
I have worked with the presentation file shared by you and have been able to observe the issue specified. Actually, the 3-D rendering effects are currently not supported in Aspose.Slides for .NET at the moment and that is why the generated HTML table does not have 3D rendering effects. I have created an issue with ID SLIDESNET-34255 in our issue tracking system to further investigate and resolve the issue. This thread has been linked with the issue so that you may be automatically notified once the issue will be resolved.
We are sorry for your inconvenience,