Cannot successfully create a local binary build of the Engine that includes iOS

Attempting to create a local binary build of the Engine that includes iOS currently fails. The error message that appears ("ERROR: System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary.") is not very clear about what needs to be fixed.

1. Add the following to the Engine's BaseEngine.ini file, with the appropriate values filled in:

   [/Script/IOSRuntimeSettings.IOSRuntimeSettings]
   RemoteServerName=
   RSyncUsername=
   

2. Make sure an SSH key has been generated and applied to the Engine to allow remote building on a Mac.
3. Start a build to create a local binary build of the Engine using the following command: AutomationTool.exe BuildGraph -target="Make Installed Build Win64" -script="Engine\Build\InstalledEngineBuild.xml" -set:WithWin64=true -set:WithWin32=false -set:WithMac=false -set:WithAndroid=true -set:WithIOS=true -set:WithTVOS=false -set:WithLinux=false -set:WithHTML5=false -set:WithPS4=false -set:WithXboxOne=false -set:WithDDC=false -set:WithFullDebugInfo=false

RESULT:
The build fails during the Compile UnrealHeaderTool Mac step, and shows the error ERROR: System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary.

EXPECTED:
The build completes successfully, or a more descriptive error is provided.