I was able to reproduce this with our own app as well as with apps by other developers (e.g. Documents by Readdle).
Our app stores its data in the app group:
Foundation.FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: AppGroupConstants.appGroupIdentifier).appendingPathComponent("File Provider Storage", isDirectory: true)!.appendingPathComponent("Media", isDirectory: true)
1) Install the app from the App Store
2) Add some data
3) Manually offload the app (Settings -> General -> iPhone/iPad Storage -> *App Name* -> Offload App)
4) Backup device to iCloud
5) Reset device (Settings -> General -> Erase All Content and Settings)
6) Restore device from iCloud Backup (this is important - it works with iTunes backups)
7) Open the app. Because it was offloaded it gets downloaded at this point but the app group data is NOT restored.
This looks like a serious bug to me.
Can someone confirm this?
