Would like some extra transcoder diagnostics for this error and if a possible a 5-minute clip file that you can get the failure on
Using RegEdit
Locate HKEY_CURRENT_USER\Software\Plex, Inc.\Plex Media Server
Click on Plex Media Server in left side area
Right click and select New \ String Value
Name the new string item TranscoderLogLevel and give it a value of verbose
Click OK and exit it RegEdit
Restart the Plex Media Server to get fresh logs created
And let me have the zipped logs on getting the failure
And the clip file that the issue was reproduced with
Please upload to dropbox or google drive etc and share link