Through the screenshot, I am not able to see if any text is missing. Could you share a screenshot from InDesign as well (of the same document) so that we can compare? With this, please share the details of the operating system you work on? Also, confirm if the issue is specific to this file and not happening with others (you can try exporting another InDesign file to see this).
Which PDF viewer do you use to view the PDF? Have you tried viewing the PDF in multiple PDF viewers and resulted in the same? If not, please test this. Would you mind saving the file as IDML > Opening the saved IDML > Exporting again and checking if this is helping? Moreover, please try testing this issue in the latest version of InDesign i.e., 20.1.
If none of the above works, please share the file with us to test.