Hi Jasparina,
The third part of font is possible to be changed after updating.
Please do following steps to revert to 16.24 version of Office and see if the fonts show up.
1.Go into one of the office Apps and choose Help > Check for Updates at the top of the screen. Turn off automatic updates.
2.Find the previous version of the particular application you want to revert (PowerPoint) on the Office Update History page:
Release notes for Office for Mac.
3.Before opening the update package, delete the application (PowePoint) from your Applications folder in the Finder. It will go to the trash (in case you need to restore it).
4.Open the installer package and it will re-install the previous version for you.
If the font appear in the presentation, Please upload them to your OneDrive for backup.
Regards,
Eric