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As of iOS 9, and in an old iOS 8.3 beta seed (12F5047f), but not the GM version of iOS 8.3, I often see crashes when using NSFetchedResultsController fetchedObjects. For example, when creating an NSSet from them or filtering them with an NSPredicate it often crashes. In both of these cases the code is running from viewDidDisappear but that's probably just a coincidence.My Core Data stack is set up to have a main queue context and private queue context both connected directly to the persistent store coordinator, with changes from the private queue context being merged with mergeChangesFromContextDidSaveNotification (plus a workaround for NSFetchedResultsController when using this setup).Has anyone else been seeing this behavior? I can't get it to reproduce with the debugger attached but it happens frequently with regular usage.

I've noticed a few crash reports for my app for "blown fences" in the iOS 11 GM. What does this mean, and what can be done to diagnose it?Here's a sample report:Date/Time: 2017-09-13 08:44:59 +0900 OS Version: iPhone OS 11.0 (Build 15A372) Architecture: arm64 Report Version: 26 Data Source: KPerf Lightweight PET Kernel Cache: 0xffffffe000000000 8447D90A-6C97-D52A-75DD-B17802154197 Reason: Fence-hang-PROCESSNAME: 530ms handling fence, blown-fence (fence duration=533ms) Command: LINE Path: /private/var/containers/Bundle/Application/5C0186AB-45F5-41EC-AD4E-E062C31F9033/APPNAME.app/APPNAME Identifier: BUNDLEIDENTIFIER Version: APPVERSION Parent: launchd [1] PID: 288 Duration: 0.55s Steps: 11 (50ms sampling interval) Hardware model: D10AP Active cpus: 2