iCloud contacts suddenly have no detail on my Mac

I use iCloud to sync contacts on my Mac Mini running macOS High Sierra 10.13.3, my iPhone X running iOS 11.2.6, and my 9.7" iPad Pro running iOS 11.2.6. Haven't had any trouble to speak of until today.

This morning, when I booted up my Mac for the first time after activating my new iPhone X and turning on iCloud, suddenly none of my iCloud contacts have associated cards when viewed on my Mac. Let me repeat that: the contacts still appear to be there -- i.e., when I click "iCloud" in the Mac's Contacts app, all of my contacts' names are visible -- but when I click each of them, there's no card. No data whatsoever in fact. Because of this, the Messages app now just lists everyone by phone number. It's as if the contacts database suddenly became corrupted -- only on my Mac.

Yes, I've clicked the contacts checkbox off and on again.

Yes, I've logged out of iCloud and back in.

Yes, I've rebooted.

And yes, my contacts appear to be completely unaffected on my iOS devices and in the cloud.

What's the next thing I should try? Is there some kind of secret force sync that's more powerful than just logging out and in? Or is there a Mac cache file that simply logging out doesn't scrub?