I found a new clue in the saving as rtf problem . The duplicate ellipse line only occurs at the end of a scene. It never occurs within the scene. At the end of the scene I put an ellipse, center it add a new blank line left justified. When saved is rtf, after my ellipse appears a left-justified ellipse I thought this was a duplicate.
I made a test chapter and saved only that chapter. LibreOffice was able to open the small single chapter. Instead of making the extra ellipse left justified it appeared as centered. Then I noticed that the extra ellipse was not a copy of my ellipse. The last ellipse of my scenes has two spaces between each star. The new ellipse has one space between each star. I do use an ellipse with one space between each star when I put an ellipse within the scene.
Could I have accidentally created an end of file marker?