If this can help, my supervisord.log file shows the following:
Created by...
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https://hub.docker.com/u/binhex/
2017-04-29 20:46:16.285514 [info] Host is running unRAID
2017-04-29 20:46:16.306854 [info] System information Linux Tower 4.9.19-unRAID #1 SMP PREEMPT Thu Mar 30 08:32:28 PDT 2017 x86_64 GNU/Linux
2017-04-29 20:46:16.329768 [info] PUID defined as '99'
2017-04-29 20:46:16.353821 [info] PGID defined as '100'
2017-04-29 20:46:16.383706 [info] UMASK defined as '000'
2017-04-29 20:46:16.406872 [info] Permissions already set for volume mappings
2017-04-29 20:46:16.430375 [info] TRANS_DIR defined as '/config/transcode'
2017-04-29 20:46:16,658 CRIT Set uid to user 0
2017-04-29 20:46:16,658 INFO Included extra file "/etc/supervisor/conf.d/plexmediaserver.conf" during parsing
2017-04-29 20:46:16,660 INFO supervisord started with pid 5
2017-04-29 20:46:17,662 INFO spawned: 'plexmediaserver' with pid 44
2017-04-29 20:46:17,821 DEBG fd 8 closed, stopped monitoring <POutputDispatcher at 47322146021176 for <Subprocess at 47322146280656 with name plexmediaserver in state STARTING> (stdout)>
2017-04-29 20:46:17,821 DEBG fd 10 closed, stopped monitoring <POutputDispatcher at 47322145874000 for <Subprocess at 47322146280656 with name plexmediaserver in state STARTING> (stderr)>
2017-04-29 20:46:17,821 INFO exited: plexmediaserver (exit status 255; not expected)
2017-04-29 20:46:17,821 DEBG received SIGCLD indicating a child quit
2017-04-29 20:46:18,822 INFO spawned: 'plexmediaserver' with pid 48
2017-04-29 20:46:18,966 DEBG fd 10 closed, stopped monitoring <POutputDispatcher at 47322145327224 for <Subprocess at 47322146280656 with name plexmediaserver in state STARTING> (stderr)>
2017-04-29 20:46:18,966 DEBG fd 8 closed, stopped monitoring <POutputDispatcher at 47322146021176 for <Subprocess at 47322146280656 with name plexmediaserver in state STARTING> (stdout)>
2017-04-29 20:46:18,966 INFO exited: plexmediaserver (exit status 255; not expected)
2017-04-29 20:46:18,966 DEBG received SIGCLD indicating a child quit
2017-04-29 20:46:20,971 INFO spawned: 'plexmediaserver' with pid 52
2017-04-29 20:46:21,168 DEBG fd 8 closed, stopped monitoring <POutputDispatcher at 47322145853952 for <Subprocess at 47322146280656 with name plexmediaserver in state STARTING> (stdout)>
2017-04-29 20:46:21,168 DEBG fd 10 closed, stopped monitoring <POutputDispatcher at 47322145874000 for <Subprocess at 47322146280656 with name plexmediaserver in state STARTING> (stderr)>
2017-04-29 20:46:21,168 INFO exited: plexmediaserver (exit status 255; not expected)
2017-04-29 20:46:21,168 DEBG received SIGCLD indicating a child quit
2017-04-29 20:46:24,173 INFO spawned: 'plexmediaserver' with pid 56
2017-04-29 20:46:24,305 DEBG fd 8 closed, stopped monitoring <POutputDispatcher at 47322146281808 for <Subprocess at 47322146280656 with name plexmediaserver in state STARTING> (stdout)>
2017-04-29 20:46:24,305 DEBG fd 10 closed, stopped monitoring <POutputDispatcher at 47322145326072 for <Subprocess at 47322146280656 with name plexmediaserver in state STARTING> (stderr)>
2017-04-29 20:46:24,305 INFO exited: plexmediaserver (exit status 255; not expected)
2017-04-29 20:46:24,305 DEBG received SIGCLD indicating a child quit
2017-04-29 20:46:25,307 INFO gave up: plexmediaserver entered FATAL state, too many start retries too quickly