Are you able to download the presentations and run them in native PowerPoint?

I have found over the years that the web-based readers are sometimes problematic.  I try to avoid using browser-based readers for MS-Office documents (regardless of the Office program) whenever possible.

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Brian - Windows 10 Pro, 64-Bit, Version 2004, Build 19041  

The purpose of education is not to validate ignorance but to overcome it.
       ~ Lawrence Krauss