Another user recently experienced something similar, but in their case the audio codec was TrueHD. Any time they played the file with the TrueHD stream selected, Plex would transcode the HEVC stream to H.264 as well as transcoding TrueHD to E-AC3 (I believe). However, the same file also had an AC3 stream available; if it was selected, both the HEVC video and AC3 audio streams would direct play. The assumption was that this proved the client was capable of direct-playing the HEVC video, and that something about having to transcode the audio was forcing the video to transcode as well. Perhaps a profile/container/codec mis-match issue?
I’m not sure if it will be useful, but here’s the other thread. There were some server logs included there (I don’t think client logs were asked for or provided). The issue seems similar, but may be entirely unrelated. The client was Android-based, but not a Shield.
