Message containing password has been suppressed error

In my experience, this error was caused by me manually editing the unattend.xml file associated with an imported operating system. Specifically, I had manually entered the UnattendedJoin credentials within the unattend.xml file. Apparently when you manually enter the credentials in there, and they are in plain text, this error will occur when you override those credentials in the customsettings.ini file. To fix this, either re-import the operating system image or make sure the plain text credentials match in both the customsettings.ini and the unattend.xml files.