Heading Style Misapplied to Body Text

This usually means the final line of Chapter 28 and the Chapter 29 title are not separate paragraphs. A manual line break (Shift+Enter) separates them, so Word treats both lines as one paragraph. Applying Heading or Normal then affects both.

Turn on Home > Show/Hide ¶. At the boundary, a bent arrow indicates a manual line break; ¶ indicates a paragraph break. Put the cursor at the end of Chapter 28’s final sentence, delete the manual break, and press Enter. You should now see a paragraph mark after the body text and another after the heading.

Click in the body paragraph and apply Normal. Click in the Chapter 29 paragraph and apply the Heading style used for other chapter titles. It should return to the Navigation Pane. If separate paragraph marks already exist, select each paragraph individually before applying its style and ensure the selection does not cross the boundary.