Recently I worked on a desktop system that was having issues connecting to WSUS and installing patches. This was a Windows 10 system (upgraded from Win 8.1) with Office 2016 (upgraded from Office 2013). Every time that I opened the Windows Update app, it listed several Office 2013 updates that couldn’t install. You could press the Retry Now button and it would run for a minute or two, but always fail with a non-specific and non-helpful error.
After running through troubleshooting steps of resetting the Windows Update agent, I finally started looking at the Office 2013 aspect. I decided to uninstall whatever 2013 components were still there and reinstall, if necessary. I loaded Programs and Features and Office 2013 was not listed.
I found a Microsoft utility to forcibly uninstall Office 2013/2016 products (link) and ran it on this PC. On the first run (and subsequent reboot), Office 2016 was removed, but 2013 was still detected by the Windows Update agent. On the second run (and subsequent reboot), Windows Update installed all of its normal patches without the Office patches listed.
I reinstalled Office 2016 and was able to bring the computer up to date. It really appears as if the 2016 upgrade didn’t fully remove all of the 2013 components as a part of the upgrade.