My contacts are out of order

Since installing High Sierra, cards added to Contacts appear in random places, not in alphabetical order. I don’t use iCloud. How can I sort them again?

Your problem lies not in the Contacts app, but its Address Book database. If you were sharing contacts using iCloud, a good approach would be to turn off Contacts in iCloud’s preferences, remove entries when offline, then turn it back on and give your Mac time to resync.

You can do similar without the help of iCloud, but must ensure that you have a good recent backup, in case it fails. Open Contacts, select All on My Mac in the sidebar (choose View > Show Groups if they aren’t shown) and choose File > Export > Contacts Archive. Make at least one safe copy of that exported file.

You then need to choose between two ways of emptying your old address book: you can select all the entries in Contacts and delete them, or quit the app and trash the folders in ~/Library/Application Support/ AddressBook, which is more radical.

With Contacts open and empty of contacts, choose File > Import to recover all your contacts from a copy of the archive you created earlier. If anything goes wrong when attempting this, quit the app and restore the whole of your AddressBook folder from your Time Machine backup, and you should be back where you started.