@Scott Craig
Thanks for your posting on Q&A.
It seems that the Custom Settings rules not configured correctly. The below setting is your environment.
DomainAdmin=<user with domain join privilege>
DomainAdminDomain=<domain name>
DomainAdminPassword=<the password for the DomainAdmin user>
JoinDomain=<domain name>
MachineObjectOU=<OU path that the device would join to>
I double confirm the Official Document of the MDT, the reference is below:
JoinDomain=contoso.com
DomainAdmin=CONTOSO\MDT_JD
DomainAdminPassword=pass@word1
MachineObjectOU=OU=Workstations,OU=Computers,OU=Contoso,DC=contoso,DC=com
It seems that there is no such DomainAdminDomain attribute. Please edit the Custom Settings rule as the Official Document and reimage the devices. Then we could confirm whether it is helpful.
In addition, please provide the NetSetup.log for me to research further if the above isn't helpful.
Best regards,
Rita
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