Yesterday I bumped into a weird issue. I've got an application that was previously only available on iOS, however I'm now creating a version for MacOS.
As I released the "working" application to TestFlight, a friend of mine told me that they don't see any of their data in the mac application. Thus, I started to investigate, and found out that on the Testflight version, the initial sync fails to sync data that didn't exist before the installation.
However, in the debug version of the application (directly ran from XCode) the initial sync syncs all data, and after downloading the production version from TestFlight it works like a charm.