Powerpoint content add-in with iframe contains website cannot be export in web version

Question

I am developing an add-in for Powerpoint. It's a content add-ins that display an external link in an Iframe.

In the desktop version of Powerpoint, everything works fine, including export and print. But in the web version, when I try to export the slides to PDF or print, the content is always blank.

I find that it happens with every website link, not just the website that I tried to display.

Does anyone know what might have caused this and how to resolve it?

Thanks