I chose a Gemini model in Settings, but my book was written with another model. Why?

When the model you chose is busy or has reached its free limit, BookyAI can let another Gemini model write the chapter so the book still gets done. From version 1.9.21 this is never silent: the progress line says "Chapter N written with ...: your ... was not available", and the chapter's engine label on the book's page turns amber (hover it to read which model wrote it and which one you wanted). Regenerate the chapter later to try your model again. If you never want another model, open Settings and, under "If my engine fails", choose "Stay on my engine": BookyAI then waits and tries your model again instead of switching.