Sudopian ok, that makes more sense now; sounds like fallback is set to be from unavailable track down to AAC which will be guaranteed to be available (all ATV stuff have AAC).
What you’re asking for is the fallback path of Atmos -> AC-3 -> AAC instead of * -> AAC @Wilson.Wang
It’s not a bug per se, so not sure how urgent a resolution be rushed by the devs. I guess you can just download low resolution video track with the correct audio track and remux manually (ffmpeg, mkvmerge, and MP4box(?) come as part of SF already) in the mean time…