https://www.theregister.co.uk/2017/10/13/apple_ios_11_crashes_garageband/

Apple is working on a fix for a bug in iOS 11 that prevents some peeps from running GarageBand.

The iPhone maker says fans have reported the music-making application no longer launches properly after installing the new iOS update with iCloud integration switched on. Disabling iCloud access for GarageBand, through the iCloud menu in Settings, allows the application to run, but users won't be able to access any GarageBand songs stored on iCloud.