I have worked with the presentation file shared by you and it seems to be an issue with Aspose.Slides while recognizing table inside presentation. An issue with ID 30909 has been created 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 is resolved.
Moreover, I have created the presentation using PowerPoint 2007 and saved that as PPT. The table is correctly read for me. For your kind reference, I have shared my sample presentation. Can you please try this on your end and also try generating the new template presentation. If the issue still persists then please share the PowerPoint version and Operating System details with us.
We are sorry for your inconvenience,