These are the sorts of things that will happen in prerelease software. Gabriel Aul, leader of the Data and Fundamentals Team at Microsoft and blogger for the Windows Insider Program, announced on Twitter that today's Windows Update for Internet Explorer may not install if Office is also install. The workaround is, if the update fails, to uninstall Office, apply the update, and then reinstall Office. Unfortunately, I am not able to give my personal experience because I use LibreOffice (I did not want to purchase a commercial license of Office).
I was not expecting to use this fail-bandaid image again, so soon.
If it wasn't an important security update, another option would be to wait for the next build. I know that, when I first installed Windows 10, I had a similar problem with a Defender update that continually failed. The install failure was fixed when I upgraded to Build 9860. The next version of Windows 10 is probably not too far away… … but this is a security update.
Hopefully this is one less thing to break when it hits full release next year.