Beware: iPhones with mixed FairPlay app ownership may no longer backup/restore as expected

Ran into this with a friend’s devices. He was syncing his and his wife’s iPhones to iTunes under Lion. Not sure how old iTunes library was.

When his wife’s iPhone 6s had to be replaced he found he couldn’t restore from iCloud backup or from his old iTunes backup (Lion OS, I didn’t check his iTunes version). He tried to create a new iCloud backup but that removed  the old one and created a 0kb backup. I couldn’t get iCloud backup working either.

Probably relevant: they had mixed app ownership, some purchased under his Apple store ID, some under her Apple store ID.

I created a backup to a fresh user account iTunes instance on my El Cap machine (but, significantly, my machine is authorized on my App Store ID). Restore seemed to proceed — but app restore didn’t complete from the iTunes backup. Instead it slowly proceeded via iCloud then left apps in dim icon status.

I believe I got things working by signing them up to Family Sharing. Then apps downloaded from iCloud, but not from iTunes.

At the time I write this I’m still investigating media rights and have yet to attempt another iCloud backup.

I wonder if Apple quietly updated its backend DRM rules.

DRM is nasty stuff.

Update:

1. The iCloud backup problem was an unrelated bug. “The Last Backup Could Not Be Completed” bug has many causes, but sometimes it’s just the wrong error message. Instead of saying “buy more storage” (which is what I usually see) iCloud Backup gave a useless error message and quit. I excluded her 5.1GB of images and it resumed.
2. Her new phone has no media. I think I know what happened. She gets her media from a non-DRMd old school iTunes music library. If you backup, as we did, from her phone to a Library on my computer there’s a DRM conflict. Apple’s iTunes DRM is device based, not (AFAIK) user account based. So my Mac wasn’t authenticated to hold her music (maybe I could authenticate, but that’s scary). I think the music got backed up, but iTunes could’t display/handle it, so it wasn’t part of the restore. The bug here is absence of an error message, simply media free restore.