Upgrade Little Snitch Before Upgrading to Mojave Beta
If you have the current release version of Little Snitch (4.1.2) installed under High Sierra, upgrade it to the latest nightly build before upgrading to the macOS Mojave beta or your system will lose network access.
If, like me, you did upgrade and lose network access, the workaround is simple: uninstall the release version of Little Snitch (make sure you keep your rules and settings) reinstall the nightly build.
To uninstall Little Snitch, run the uninstaller app and follow the on-screen instructions.
You can run the uninstaller from Terminal with the following command:
/Library/Little\ Snitch/Little\ Snitch\ Uninstaller.app