Apple managed to introduce yet another bug in the security fix they shipped yesterday, it's benign but even so.
https://www.macrumors.com/2017/11/29/apple-macos-high-sierra-file-sharing-fix/
Update: Apple appears to have released a revised version of the security update, which is valid for systems running both macOS 10.13.0 and 10.13.1. The revised version may also address the issue in the original version that resulted in file sharing problems.
Is there anyone actually testing things at Apple?