Alignment is wildly off for one book -- audiobook was downloaded as xHE-AAC

Alignment had been accurate for every book until one where the readaloud is so far out that I cannot tell where in the audio it thinks it is. I had also noticed playback oddities with the raw audio file on its own. The audiobook was downloaded with Libation, and I wondered whether I needed a larger transcription model.

Resolution: Check the audio codec before reaching for a bigger transcription model. Audiobooks downloaded with the xHE-AAC option enabled (for example Libation's xHE-AAC setting) do not decode correctly under ffmpeg, so what Storyteller transcribes bears little relation to the actual narration and the resulting alignment is nonsense; the same files usually also glitch in ordinary players, which is the tell. Fix: re-download the audiobook with xHE-AAC turned off (plain AAC/M4B) and recreate the readaloud -- that resolved it. If the setting was enabled for a while, audit the rest of your library, since the failure is per-file and easy to miss until you actually read the book. Also confirm you are aligning matching editions: an abridged, dramatized or graphic-audio recording will never align against an unabridged ebook.