Found multiple posts about this error, but it took days of troubleshooting to finally fix. The error means "Path not found" and I was getting it when the SCCM client was trying to deploy. The SMSTS.log was no help while in WinPE, and no errors in any of the server logs.
SMSTS.log did update after rebooting and logging into Windows. Come to find out it's failing looking for a local file, but I couldn't figure why it was looking to the wrong partition when I have the OSPART variable setup.
=============================[ OSDSetupWindows.exe ]===========================
Command line: "OSDSetupWindows.exe"
Running module version 5.0.9049.1000 from location 'X:\sms\bin\x64\OSDSetupWindows.exe'
Releasing: CPD00157
Unsuccessful in releasing CPD00157. 80070490.
!shFile.null(), HRESULT=80070003 (setupwindows.cpp,823)
Failed to open file: C:\WINDOWS\panther\unattend\unattend.xml (0x80070003)
this->resolveConfigFileVariables(), HRESULT=80070003 (setupwindows.cpp,423)
setup.run(), HRESULT=80070003 (setupwindows.cpp,1652)
Exiting with code 0x80070003
Process completed with exit code 2147942403
!--------------------------------------------------------------------------------------------!
Turns out the issue was a Restart happening earlier in the task sequence! The restart was for a BIOS update on a different model of laptop, but that restart was changing the partition info when it rebooted and making CCMSETUP.exe look for a different partition. I removed that reboot and issue resolved.