For some reason the String evaluation returns a negative number.
[Success] Retrieve - Sucessfully retrieved the directory size from: [%BaseDir%\Custom\x64\IsoRoot] to variable: [%IsoRootSize%] with result: [-1460156359]
[Ignore] IF - [-1460156359] is not bigger than
evaluated string: [If,%IsoRootSize%,Bigger,0,Begin]
Evaluation of the string returns IsoRootSize smaller than 0 so the plugin skips the copy.
There is nothing in the returned value,
You can try to rem-out the offending code in CreateISO.script
[IsoRootAdd]
//Retrieve,FolderSize,%GCustom%\%Architecture%\IsoRoot,%IsoRootSize%
//If,%IsoRootSize%,Bigger,0,Begin
Echo,"Copy Iso Root Files..."
DirCopy,%GCustom%\%Architecture%\IsoRoot\*,%GISO%
//End
Knowing UDF file system support up to 16TB, I would give it a try.