KB4038788 would not download nor install on my Asus portable. After trying many fixes, clean hard drive, trying to stop wuauserv, download the KB and manually install I finally was able to download and install after the following.
Ran Windows Update Troubleshooter which sowed a problem with Service Registration Missing or Corrupt. Troubleshooter said it was Fixed - not really.
With this problem in mind an internet search provided me with the MS page for Windows 10 Service Registration is Missing or Corrupt. That page has 2 Methods. I used Method one and it worked. Using services.msc reset Windows Update Service to Automatic and start it (mine was Manual & was started) then reset Background Intelligent Transfer Service to Automatic and start it (mine was Manual and stopped) then reset Cryptographic Service to Automatic and start it (mine was Automatic and started).
My computer then downloaded the KB and installed it normally.

Hope this helps someone else.