Every chapter failed with "outside the retail spec" and even the re-renders were identical. (fixed in v1.6.2)

If the numbers shown were very low (e.g. "RMS −60-something dB"), the chapters were actually silent: the narration engine failed once on that machine, BookyAI cached the broken audio, and re-renders kept reusing the cache.

Since v1.6.2 broken audio can never enter the cache (the render stops with a clear message naming the affected chapter instead), and re-rendering a chapter truly regenerates it.