This issue (though on a different client version) was raised by another forum user yesterday; a Plex employee was able to reproduce the problem and are working on a fix.
Regarding your DTS playback failure, this seems suspicious:
05-11 18:32:47.003 i: [ExoPlayer][EventLogger] [X] Track:0, id=1, mimeType=audio/vnd.dts, bitrate=1536000, codecs=dts, channels=6, sample_rate=48000, language=english, supported=YES
...
05-11 18:32:48.911 i: [FFmpeg] [WARN] [dca @ 0x8b45f400] Channel layout '7.1' with 8 channels does not match specified number of channels 6: ignoring specified channel layout
It seems as though the MKV container suggests 6-channel audio is present, while FFMPEG detects 8-channel audio. It could be completely innocuous; however, that logging leads up to this:
05-11 18:32:49.327 e: [ExoPlayer][EventLogger] playerFailed [eventTime=31.48, mediaPos=0.00, window=0, period=0
com.google.android.exoplayer2.ExoPlaybackException: Plex.Audio.Renderer error, index=2, format=Format(null, null, null, audio/raw, null, -1, null, [-1, -1, -1.0], [6, 48000]), format_supported=NO
at com.google.android.exoplayer2.o0.handleMessage(SourceFile:43)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:193)
at android.os.HandlerThread.run(HandlerThread.java:65)
Caused by: com.google.android.exoplayer2.audio.AudioSink$InitializationException: AudioTrack init failed 0 Config(48000, 252, 196992)
It may be worth your time to ensure you mux-ed in the audio track you intended to (or set the track properties as intended).
