Hello jaconstant,
Thank you for posting in the Apple Support Communities, and for reviewing the related article linked above. We'd like to offer our support with exporting your Keynote to Powerpoint.
We recommend following the steps in the below support article since they have resolved similar concerns in the past:
Convert Keynote presentations to PDF, Microsoft PowerPoint, and more
From there, you might consider exporting a different Keynote presentation to help isolate to something within the current document.
If this concern continues after taking the steps above, our resolution is to contact Apple Support directly. Depending on your region, you may be able to reach them here:
Get Support
Kind regards.