I'm facing the exact same issue. Tons of messages like yours. Initial sync of a dataset containing ~10.000 records (and ~100MB on disk) takes 15 minutes while the CPU hits over 100%. Honostly, it makes me reconsidering the choice to use CloudKit as the cloud-backed datastore. I talked with several engineers from Apple, both during WWDC as well as DTS, but didn't got anything useful. Hoping this thread is going to be a push in the right direction.