I don’t see in the logs why the audio is transcoding. There’s some “not supported” type messages, but nothing specific such as channel limits, bandwidth limits, etc.
I’m going to guess it has to do with Dolby Vision. DV support in Plex and with the Shield is still a work in progress. Sometimes the Dolby Vision decoder crashes on the Shield. When this happens the video plays in HDR.
Maybe the DV decoder crashing somehow affects audio as well?
Linked below is a long and still active thread regarding DV support on various platforms. You might scan it for applicable info. Note that your movie uses Dolby Vision Profile 7, and there are specific comments in the thread regarding that profile.
I’m still working on picking up the ins and outs of DV support with Plex. Maybe somebody with better knowledge on the topic can provide additional info.
