I see the issue, your profile hasn’t instructed custom command to check for the exit code:
2025-08-24T10:54:25 MCEBuddy.Transcode.CustomCommand → About to run custom command with parameters:
PreCustomCommandPath = c:\windows\system32\windowspowershell\v1.0\powershell.exe
PreCustomCommandParameters = -File “e:\plex\convertHdr10+ToAV1.ps1” -InputFile “E:\Radarr\Guardians of the Galaxy (2014)\Guardians of the Galaxy (2014).mkv”
PreCustomCommandHangPeriod = 0
PreCustomCommandCritical = True
PreCustomCommandUISession = True
PreCustomCommandShowWindow = True
PreCustomCommandExitCodeCheck = False
You need to set the CustomCommandExitCodeCheck to true in the profile if you want MCEBuddy to look at the exit codes. CustomCommandCritical just look for terminations and problems with the process itself and doesn’t look to the return or exit codes.
From the customcommand documentation: MCEBuddy - Advanced Settings, Commands and Tweaking
CustomCommandCritical, when this is set to true, MCEBuddy will fail the entire conversion if the custom command is invalid or if the process is terminated (due to hang detection). If it is set to false then MCEBuddy will continue with the conversion processing irrespective of the custom command failure/success UNLESS the converted file has been renamed or deleted. By default the value is false.
CustomCommandExitCodeCheck(v2.4.1+) is set to true if you want MCEBuddy to check the Exit Code of the custom command application. If the return code is 0 (default) it is considered a success, if not 0 (+ve or -ve) then it is considered a failure. If the Exit Code fails MCEBuddy will stop further processing and fail the conversion.