Windows 10 1803 Unattended Install Fails

I've been doing Windows unattended installs successfully with Windows 7 and earlier versions of 10. Currently, I'm attempting the same with version 1803 (USB installation media) on a new motherboard.

The installation shows the EULA (should be hidden) and, after that is accepted, shows the following error:

"Setup was unable to create a new system partition or locate an existing system partition. See the setup log files for more information."

There is one record in setuperr.log:

2020-03-04 09:43:07, Error      [0x060549] IBS    Install drive does not meet requirements for installation[gle=0x00000057]

The pertinent records (I think) in setupact.log are:

2020-03-04 09:43:07, Info       [0x0606cc] IBS    GetSystemDiskNTPath: Unable to get required buffer size for system disk from BCD APIs; status = 0xc0000452
2020-03-04 09:43:07, Info                  IBS    GetMachineInfo:Couldn't find any system volumes on this EFI-based computer
2020-03-04 09:43:07, Info                  IBSLIB CanBeSystemVolume: Volume at disk [0] offset [0x0] doesn't meet criteria for system volumes...
2020-03-04 09:43:07, Info                  IBSLIB DiskRegionSupportsCapability:Region on disk [0] (offset = [0x0]) is BLOCKED against capability [CanBeSystemVolume] for the following reasons...
2020-03-04 09:43:07, Info                  IBSLIB LogReasons: [BLOCKING reason for {disk 0 offset 0x0}: CanBeSystemVolume] The partition is too small.
2020-03-04 09:43:07, Info                  IBSLIB CanBeSystemVolume: Volume at disk [0] offset [0x4400] doesn't meet criteria for system volumes...
2020-03-04 09:43:07, Info                  IBSLIB DiskRegionSupportsCapability:Region on disk [0] (offset = [0x4400]) is BLOCKED against capability [CanBeSystemVolume] for the following reasons...
2020-03-04 09:43:07, Info                  IBSLIB LogReasons: [BLOCKING reason for {disk 0 offset 0x4400}: CanBeSystemVolume] The partition is too small.
2020-03-04 09:43:07, Info                  IBSLIB CanBeSystemVolume: Volume at disk [0] offset [0x1bf2900000] doesn't meet criteria for system volumes...
2020-03-04 09:43:07, Info                  IBSLIB DiskRegionSupportsCapability:Region on disk [0] (offset = [0x1bf2900000]) is BLOCKED against capability [CanBeSystemVolume] for the following reasons...
2020-03-04 09:43:07, Info                  IBSLIB LogReasons: [BLOCKING reason for {disk 0 offset 0x1bf2900000}: CanBeSystemVolume] The partition is too small.
2020-03-04 09:43:07, Info                  IBSLIB CanBeSystemVolume: Volume at disk [0] offset [0x100000] doesn't meet criteria for system volumes...
2020-03-04 09:43:07, Info                  IBSLIB DiskRegionSupportsCapability:Region on disk [0] (offset = [0x100000]) is BLOCKED against capability [CanBeSystemVolume] for the following reasons...
2020-03-04 09:43:07, Info                  IBSLIB LogReasons: [BLOCKING reason for {disk 0 offset 0x100000}: CanBeSystemVolume] The selected disk space is not of type ESP.

2020-03-04 09:43:07, Info                  IBSLIB CanBeSystemVolume: Volume at disk [0] offset [0x9c4100000] doesn't meet criteria for system volumes...
2020-03-04 09:43:07, Info                  IBSLIB DiskRegionSupportsCapability:Region on disk [0] (offset = [0x9c4100000]) is BLOCKED against capability [CanBeSystemVolume] for the following reasons...
2020-03-04 09:43:07, Info                  IBSLIB LogReasons: [BLOCKING reason for {disk 0 offset 0x9c4100000}: CanBeSystemVolume] The selected disk space is not of type ESP.

2020-03-04 09:43:07, Info                  IBSLIB Remedy was applied for said disk rule
2020-03-04 09:43:07, Info                  IBS    InstallDestinationMeetsRequirements: Unable to find/create system volume or system volume doesn't meet criteria for installation; hr = 0x80300015
2020-03-04 09:43:07, Error      [0x060549] IBS    Install drive does not meet requirements for installation[gle=0x00000057]
2020-03-04 09:43:07, Info                  IBS    There was a failure applying the ImageInstall/OSImage/InstallTo unattend settings (or WillShowUI=Always).  Setup will display the UI to select an image install destination.
2020-03-04 09:43:07, Info       [0x0640ae] IBSLIB PublishMessage: Publishing message [Setup was unable to create a new system partition or locate an existing system partition. See the Setup log files for more information.]
2020-03-04 09:43:07, Info                         This installation is blocked from completing due to compliance failures or invalid input; this is not an internal error.
2020-03-04 09:43:07, Info       [0x0a013d] UI     Accepting Cancel. Exiting Page Progress.
2020-03-04 09:43:07, Info                  UI     Entering Page Cancel.
2020-03-04 09:43:07, Info       [0x0a0035] UI     Allowing Page 'EULA' to be shown
2020-03-04 09:43:07, Info       [0x0a0035] UI     Allowing Page 'EULA' to be shown
2020-03-04 09:43:07, Info       [0x0a011c] UI     WizardDialogPost::SetActive

The USB installer was created using a downloaded ISO file from Microsoft and Rufus to apply it to the USB drive. The installer works when used manually, just not in conjunction with autounattend.xml.

Further possibly useful info:

• Two installation drives have been tried, SATA and mSATA SSDs
• I tried rebuilding the answer file with the corresponding Windows ADK

Any other information needed, just ask.

Thanks for any and all feedback.