Are you sure it's not what Microsoft noted below?
"Even though the update was successfully installed, Windows Update incorrectly reports that the update failed to install. Select Check for Updates to confirm that there are no additional updates available.
You can also type About your PC in the search box on the taskbar to confirm that your device is using the expected OS build.
Microsoft is working on a resolution and will provide an update in an upcoming release."
https://support.microsoft.com/en-us/help/4088776/windows-10-update-kb4088776
For some time now Windows 10 update KB4088776 won't install but it keeps coming up in windows update. Today I have been updating several computers in the house to the new April 2018 update but this one laptop has the problem with update KB4088776 which seems to block the April 2018 update from showing up. How do I skip this KB4088776 update so I can get to the new April 2018 update.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic