This is because the HTML code has incorrect data in it and is not rendering correctly on the Report Card.  This could be caused by Copy & Pasting from another source such as a Google/Word document. To fix this navigate to:
  1. onRecord > Performance > Grading > Report Card Builder > 
  2. Select the School Level the Report Card is built in
  3. Click Edit next to the Report Card having the issue
  4. Remove any coding that does not seem relevant, or if you have Introductory Text working on another Report Card that is exactly the same, you can click Edit next to the working Report Card and click HTML in the Introductory Text. Copy the HTML code and replace the HTML within the Report Card that is not working correctly
  5. Click Save