It appears the problem is that the fixes included in the security updated were n...

alphabettsy on Dec 2, 2017 | parent | context | favorite | on: MacOS Update Accidentally Undoes Apple's “root” Bu...

It appears the problem is that the fixes included in the security updated were not backported to 10.13.1 which caused a problem for users coming from 10.13.0 that had done the security update. Certainly a huge issue, but many commenters seem to misunderstand the article.