I just finished fixing the same issue with my app. I had the exact same issue. The app worked fine when running from the simulator, but crashed with the lightweight migration error when running from a tethered device. In my debug output, noticed that the "file:///var/mobile/Containers/..." path indicated that the model file was saved to an App Group (I share data with a widget extension). In order to fix the issue, I created a new App Group and this fixed the problem.