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