• OS: Windows 10 1709
• PowerShell Version: 5.1.16299.98 (Desktop)
• List the steps to reproduce the problem below (if possible attach a screenshot and/or link to the code): In all my builds the GUID is 00000000-0000-0000-0000-000000000000

Examples:

• All updatable Help Files located in \release\X.X.X\en-US (And the general release folder)
  CAB: et.General_00000000-0000-0000-0000-000000000000_en-US_HelpContent.cab
  ZIP: et.General_00000000-0000-0000-0000-000000000000_en-US_HelpContent.zip
  XML: et.General_00000000-0000-0000-0000-000000000000_HelpInfo.xml
• The general MD File (Header) in /docs
  In your case: ModuleBuild.md contains Module Guid: 00000000-0000-0000-0000-000000000000

As a Workaround a run a cleanup script after each build to rename the files and replace the MarkDown Header based on the real Guid from the Manifest.