Symantec Support Response below:
From my research, both Device guard and Credential guard has just been recently release and are being made available to install on the first release of Windows 10.
The latest release of 12.1 RU6 MP4 was release prior to the release of these programs and therefore the latest release 12.1 RU6 MP4 is not compatible with these 2 new security features of Windows 10.
Windows 10 Preview (the new release of Windows 10) these features will be built into Windows 10.
We will be releasing 12.1 RU6 MP5 that will be compatible with the new release of the Windows 10.
When version 14.1 is released, it will have all the fixes for the new release of Windows 10 and other releases of Windows.
Since these are designed to be released with the new Windows 10 version that is due to be released at the end of the summer, Symantec has not created a document referencing these issues.
The solution at this time if you desire on Device Guard/Credential Guard installed on the system is to remove ADC from the client. There is a conflict between the drivers that is being worked on by our developers.