iOS 13 beta was nice to use all summer, but next week I’ll need my new phone to restore from a backup. That means I needed to make a backup on the public release version, the GM. This year it’s complicated because the beta channel is currently on 13.1, not 13.0, so it’s a downgrade. And because that’s something you’re never supposed to have to do, I had problems.
After downgrading iOS from 13.1 beta to 13.0 GM, my Mail database seemed to fail to load. The app would freeze for about six seconds after tapping most any mailbox, and then the mailbox list would be empty. It was as if loading from the message cache caused a failure, like a crash and restart in whatever daemon owns the data. The only exception was an inbox I had zeroed before the upgrade, which worked fine.
To fix that I wanted to reset my Mail cache, for which there are no explicit controls. It wasn’t enough to remove my Mail accounts and delete the app and add them back. Thinking a cache wouldn’t be included in backups (and it should be only a cache because these are IMAP accounts), I backed up my phone on 13.0, erased all content and settings, and restored. That did the trick for Mail.
An hour later I found my music library was suffering from a similar problem, and no amount of tricks would solve it. Although I could add and remove files through means like iTunes sync, the library index appeared to be missing a lot of them. The index was immutable, for instance, I couldn’t add a song to a playlist or add from Apple Music. This was also true for Podcasts and TV. I imagine they are still one big database under the hood.
I think the reason having restored from a backup made no difference to the media library is that it is not simply a cache, it’s a source of truth. Syncing through iCloud Music Library is optional, so the backup mechanism probably needs to include the index even though it omits the media files.
I had to preserve some data, do a fresh install, and then set everything up again from scratch. Ultimately the amount of time that took was about the same as the amount of time I spent trying to repair things. It would have been simpler to just reset to a state I could be confident in.
If any of that made your stomach turn, don’t tempt fate by putting a beta on your carry phone.