I was not synchronizing with anything but iCloud. Before the recent update that fixed it, I was in the habit of disabling WiFi when on battery so that my laptop

I was not synchronizing with anything but iCloud. Before the recent update that fixed it, I was in the habit of disabling WiFi when on battery so that my laptop would not drain my battery. contactsd definitely was doing something dumb around synchronization. At one point, I backed up my ~8,000 contacts and deleted them all. Everything was fine until I restored them.