I could easily affect just one paragraph in 274 pages - it just depends on where your section breaks are. Does the issue appear on your machine using the file you posted here to check? Or was it resolved by creating that cut down file?

Your approach of three soft returns around a chapter title is a novel solution to avoiding indents on two paragraphs and the majority of Word users would approach that same requirement by using either:
1. local paragraph settings via ruler or Paragraph format dialog
2. styles

If it were me doing it, I would choose styles for the speed, flexibility and consistency it brings but it 'can' be done your way as long as you are prepared to put in the time and effort to make all the content consistent. 274 pages is a massive amount of work to standardise without styles.

I'm also surprised you are using continuous section breaks with different odd/even pages and first pages. How many section breaks are in your document?

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Andrew Lockton
Chrysalis Design, Melbourne Australia