When you find one, bugs will necessarily be multiple. If you think you’ve found one, you can be fairly confident that you’ll find more. Four bugs in macOS for the price of one.
Changes include frequent timechecks by timed, harder access to info about keychains, a couple of possible AppleScript bugs, and APFS snapshots.
High Sierra has done away with the ntpd daemon for keeping your Mac’s clock in sync with a standard time server. This now works as in iOS, using the timed daemon.