ICloud does not work in the application on a real device.
When tested in a simulator, everything works fine.
I viewed id applications on developer.apple.com, there is iCloud enabled. As soon I upload the application on itunes connect, and invite people into testflight, then nothing works.
Maybe need include something on the website? Or some phone settings? Or at developer.apple.com something else is needed?
You have to enable iCloud for distribution in your App ID in order for it to work on devices distributed through Test Flight. This will then enable it on the devices where it was installed through Test Flight.
Hope that helps,
Julian