This only happens with some templates and fonts and I still haven’t found a solution :-(

If you have access to an installed version of PowerPoint you can try embedding the fonts in the presentation, then re-upload it to OneDrive. Here are the steps:

1. Choose File>Save As>Browse.
2. In the Save dialog, click on Tools>Save Options and check the Embed fonts in the file.
3. Choose the Embed all characters option, then click on the OK button.

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