DirectStream means the video is just being passed through.
The transcode is on the audio, which means your Shield has a bad setting somewhere. If you have night mode listening activated on Shield that will cause a transcode. Either way, this is not a Plex issue.
I can confirm night audio is disabled, dolby audio processing is also off and my plex app is set to HDMI passthrough. I’ve had the same settings for as long as I can remember and never had an issue in the past. So I am not really sure what else there is to change or what might be causing the transcodfing to happen
I have found if I select my audios available formats in the shield and set it to manual enable all of the audio options I get direct play on everything. As soon as I turn off dolby vision audio or use the Automatic function, I get transcodes everywhere.
Why has this changed? I always had all of this off and had the audio formats set to ‘Auto’
(not my image below just one I found online to show the section I am talking about)