Server Version#: 1.23.1.4528
Player Version#: 8.17.0.25120
For some reason this version of Black Panther will not direct play via my Fire TV Cube. It is showing as an HEVC Rext H264 file.
It will direct play the audio, but is transcoding the video, as you can see.
It may be that the Cube and/or your TV does not support the video format, so Plex transcodes it to H.264.
Pull up the Media Info window for the movie and look at the Bit Depth and Chroma Subsampling.
Most HEVC movies are 8- or 10-bit, with 4:2:0 subsampling.
RExt = Range Extensions and are additions to the HEVC specification. They support capabilities such as additional bit depths and chroma subsamplings (4:0.0, 4:2:2, 4:4:4).
The Amazon Cube device specs do not mention chroma subsampling.
Look for lines with Media Decision Engine or MDE (also any nearby entries). The server log zip file contains many individual files. Look in Plex Media Server.log (most recent) - Plex Media Server.5.log (oldest).