Core Data lightweight migration crashes after App update

Question

Two days ago I released the App. According to feedback on AppStore and crash reports from itunesconnect there are a lot of crashes on launch. But not 100% users suffered, only 30% maybe.

I've read the crash logs and saw a problem. It's crashing on DB migration process. I use lightweight migration of database. Usually I add new datamodel version very carefully. Even before each release I install a previous version of the App, use it for some time and only then I install the latest version above it. So was this time.

I looked through two datamodels (previous and present). Were added:

1) New entities (it's OK for lightweight migration)
2) New fields inside existing entities. All they are optional. (OK for lightweight migration)
3) One new field in existing entity which I made optional AND indexed. (OK?)

None of existing fields and entities were renamed.

What I did wrong?

Stack trace:

Thread 0 name:  Dispatch queue: com.apple.main-thread
Thread 0:
0   libsystem_kernel.dylib          0x352f439c pread + 20
1   libsqlite3.dylib                0x30d2d632 unixRead
2   libsqlite3.dylib                0x30d4221a readDbPage
3   libsqlite3.dylib                0x30d41156 sqlite3PagerAcquire
4   libsqlite3.dylib                0x30d583be moveToChild
5   libsqlite3.dylib                0x30d8e0e8 moveToLeftmost
6   libsqlite3.dylib                0x30d59582 sqlite3BtreeNext
7   libsqlite3.dylib                0x30d54328 sqlite3VdbeExec
8   libsqlite3.dylib                0x30d4f6c2 sqlite3_step
9   CoreData                        0x329e8e2e _execute
10  CoreData                        0x329e8d64 -[NSSQLiteConnection execute]
11  CoreData                        0x32a8bd54 -[NSSQLConnection prepareAndExecuteSQLStatement:]
12  CoreData                        0x32add63c -[_NSSQLiteStoreMigrator performMigration:]
13  CoreData                        0x32ad42b8 -[NSSQLiteInPlaceMigrationManager migrateStoreFromURL:type:options:withMappingModel:toDestinationURL:destinationType:destinationOptions:error:]
14  CoreData                        0x32a79c02 -[NSMigrationManager migrateStoreFromURL:type:options:withMappingModel:toDestinationURL:destinationType:destinationOptions:error:]
15  CoreData                        0x32ac5bf4 -[NSStoreMigrationPolicy(InternalMethods) migrateStoreAtURL:toURL:storeType:options:withManager:error:]
16  CoreData                        0x32ac519c -[NSStoreMigrationPolicy migrateStoreAtURL:withManager:metadata:options:error:]
17  CoreData                        0x32ac6b58 -[NSStoreMigrationPolicy(InternalMethods) _gatherDataAndPerformMigration:]

Answer 1

Any chance that those users were more than one .xcversion back? Core Data will not "chain" your upgrades for you. So if you have V1, V2, and V3, and V3 becomes the current version, anyone at V1 will not be upgradable. It is possible to add in your own code that helps "step it through" V1 to V2, then V2 to V3. I believe Marcus Zarra's "Core Data" book had example code that does that.