NSUserDefaults Broken System-Wide

Number:rdar://26642019 Date Originated:6/5/2016
Status:Open Resolved:
Product:iPhone 6s Plus, AT&T Product Version:iOS 9.3.2 (13F69)
Classification: Reproducible:
Apps that rely on NSUserDefaults to keep the user logged in fail and log the user out. In addition, apps that rely on NSUserDefaults to store data cannot access or synchronize data.

This has happened twice for me in under a month (first time on iOS 9.3.1), only resolution is to do a complete restore and start from scratch. No crash logs produced.

Steps to Reproduce:
This issue appeared after building an app saving NSArrays to NSUserDefaults. It appears to relate to the synchronize command, as after this bug starts the synchronize command will no longer work (along with accessing anything from NSUserDefaults).

Expected Results:
NSUserDefaults can be used to set objects, along with synchronizing new data.

Actual Results:
NSUserDefaults gets completely broken, both reading and writing. This results in a user being logged out of apps (ex: Facebook, YouTube, Inbox by Google). Relogging into apps will log in for ~24hrs, then will NSUserDefaults will attempt to save on a per-app basis but fail, resulting in the user being logged out. NSUserDefaults fails.


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