To troubleshoot this issue, you may do the following steps:

1. Check that all the text boxes are styled with the desired font and font size.
2. Ensure that your text boxes are not marked as hidden, either through manual manipulation or in the overall presentation theme.
3. Check to make sure that your text box is positioned above any layered shapes
4. Verify if the issue persists when the presentation is viewed by another browser.
5. If the issue persists, try donating a copy of the presentation.