1. Check the fonts used for the inserted symbols. Make sure that the correct font type is embedded in the presentation.
2. Check applicable software updates. Make sure that the office suite you are running is up-to-date.
3. Check display settings. Make sure that your presentation is set to display fonts and objects correctly.
4. Try reducing the resolution of the presentation. This may solve certain display issues.
5. Refer to online support or contact technical support if the issue persists.