A family of Microsoft word processing software products for creating web, email, and print documents.
Reinstalling is a last resort on a Mac. This is especially true if the issue is evident only in particular documents. Test in a new document to see whether the same issue is evident.
Before anything else go to Word> About Microsoft Word in the main menu to determine the present Version & type of License for your Office software. Include that info in your reply. Indicate your specific update level of Mojave as well.
Also, go to Word> Preferences> Track Changes to confirm what the settings are for Balloons at the bottom of the Preferences pane.