I am also facing this issue of the installer being 16 MB. I tried several times but out of luck. Then I downloaded the DMG file from this website, [MacOS High Sierra 10.13.6 DMG direct download [Updated]][1] and then used it to update my system. Apple really needs to fix this annoying issue.


  [1]: http://hackintoshpro.com/macos-high-sierra-dmg-download/