One of the things that you will always run into with Windows Insider builds are quirks and small troubles that surface with each new build.
In 18312 running the update via settings on a couple of my machines I observed the following error. I chose the restart and it started the install and it rolled up to the 18309 Login screen- 4 times in a row on a couple different builds, physical and virtual! This approach is not working, a quick check on some of the forums and the following approach to get the build to install works most of the time.
To address this issue, from the start menu choose the classic update and restart choice that you have seen with patches and updates through the ages, for 3 out of for machines this worked the very first time,
on one machine this keeps rebooting and keeps on bringing up the 18309 login page, nothing in the Event Viewer and nothing via setupdiag (Good for parsing all the usual log locations!) that shows of any error. This is one of those setup quirks that we see every now and again. Persistence helps get through it and
my best advice on this would be to not ram it through. I find that if you artificially force the update there is a better then even probability you will do more damage to your overall position then good. Stick with it and you will usually come out with the expected outcome - it worked for me!
Murray