When I use "Expand" in the chapter editor, the AI reuses sentences from elsewhere in the chapter. How do I avoid that?

Update to version 1.9.1 or later. Expand and the other rewrite tools now show the AI the text around your selection as off-limits — it must add genuinely new material that fits between the surrounding lines, not repeat or paraphrase them — and a result that copies whole sentences from the surrounding text is automatically redone. Tip: select a complete passage (a paragraph or a scene) rather than a fragment; the AI expands more naturally when it can see where the passage begins and ends.