I have been having the same issues although it doesn’t happen everytime 2 recordings are starting at the same time.
Found the following common entries on failed recordings in my logs:
Plex Media Server.2.log:Feb 26, 2018 12:37:37.291 [0x7fc953bff700] ERROR - [Transcoder] [stream_segment,ssegment @ 0x24c0720] sample rate not set
Plex Media Server.2.log-Feb 26, 2018 12:37:37.293 [0x7fc957ffe700] ERROR - [Transcoder] Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument
Plex Media Server.2.log-Feb 26, 2018 12:37:37.294 [0x7fc953bff700] ERROR - [Transcoder]
Plex Media Server.2.log-Feb 26, 2018 12:37:37.298 [0x7fc9717ff700] ERROR - JobManager: child process returned: 1 (Operation not permitted)
Plex Media Server.4.log:Feb 25, 2018 19:56:18.008 [0x7fe7667f3700] ERROR - [Transcoder] [mpegts @ 0x208d4c0] sample rate not set
Plex Media Server.4.log-Feb 25, 2018 19:56:18.010 [0x7fe76efff700] ERROR - [Transcoder] Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument
Plex Media Server.4.log-Feb 25, 2018 19:56:18.011 [0x7fe76dffd700] ERROR - [Transcoder]
Plex Media Server.4.log-Feb 25, 2018 19:56:18.015 [0x7fe7917ff700] ERROR - JobManager: child process returned: 1 (Operation not permitted)
Plex Media Server.log:Mar 04, 2018 15:41:19.742 [0x7f181d7f6700] ERROR - [Transcoder] [mpegts @ 0x1d03b20] sample rate not set
Plex Media Server.log-Mar 04, 2018 15:41:19.743 [0x7f18153f2700] ERROR - [Transcoder] Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument
Plex Media Server.log-Mar 04, 2018 15:41:19.745 [0x7f18409e4700] ERROR - [Transcoder]
Plex Media Server.log-Mar 04, 2018 15:41:19.748 [0x7f183fbff700] ERROR - JobManager: child process returned: 1 (Operation not permitted)
Running PMS Version 1.11.3.4803
