Something that I've been during the development of Mac Catalyst with core data + CloudKit mirror is a crash that happened for "no reason". It's something that only happened when you are running your app by Xcode, I tried to replicate this same error opening the debug version and it didn't happen. In fact, today I had 2 labs to figure out what's going on: Core data Lab, JUNE 23 TUESDAY AT 12:00 PM PDT, and JUNE 23 TUESDAY AT 1:30 PM PDT, but the bug didn't appear in both. Fortunately / unfortunately, the bug happened when I turned off the Lab call 🧐. So, here I am again! This time I uploaded to the feedback assistant the radar file with the System Information Report and here is the URL: https://feedbackassistant.apple.com/feedback/7761898 I Hope helped you guys, I'm looking forward to hearing from you.