SOLUTION: Conversion failed. The transcoder exited due to an error

There is a memory leak issue with TrueHD - see

would need logs to establish if it is the same issue

See
https://support.plex.tv/articles/201643703-reporting-issues-with-plex-media-server/
https://support.plex.tv/articles/200250417-plex-media-server-log-files/