I had the same issue and have spent the last 2 1/2 hours trying to fix it. I have used all of the suggestions given here, the Troubleshooter, Support Pages, and the Virtual Assistant. None of those worked.
Since the ONLY problem I was having was that this older update was not installing, (newer updates do without problems), I decided to just skip that and "hide it" as suggested here.
On this version of Windows 10, "Hide Update" is not an option, like it was in earlier versions of Windows. Microsoft keeps things dummy-proof and tries to protect us from doing things they don't want us to do.
However, by using the Virtual Assistant (Get Help) and doing a search for "hide update Windows 10", I found "there is an app for that".
Download the app and run it as Administrator. Restart, and go back to Windows Update. The Failed Update is still there and showing the failed error. Click Retry and it disappears and the client then downloads the next (newer) update. Since the newer update
is a "Cumulative" update, one would think that it includes, or fixes, older updates. The update information (KB info) does not state that it does, so I don't know. Your mileage may vary.
What is interesting is the description for the update that failed. Go to Update History:
2018-11 Update for Windows 10 Version 1803 for x64-based Systems (KB4023057) - Error 0x80070643
Failed to install on 1/17/2019 - 0x80070643 and click the link.
"This update includes files and resources that address issues that affect the update processes in Windows 10 that may prevent important Windows updates from being installed. These improvements help make sure that updates are installed seamlessly on your device,
and they help improve the reliability and security of devices that are running Windows 10."
So the update that will not install and fails with an error is designed to fix the problem of updates not installing and failing with an error.
OK, sometimes the Windows Update Client needs these types of fixes. BUT, "This update is not offered through the Microsoft Update Catalog." Which means you cannot download the standalone fix and must rely on the Windows Update Client to download and install
the fix.
Who's brilliant idea was that?
Anyway... if you are not having any other problems, use the App and hide the failed update and get on with your day. I think we have better things to do than to fix an operating system that should be working seamlessly in the background. <end of rant>