It seems context getting cleared in multithreading when use with core data.
Thread 3: EXC_BAD_ACCESS (code=1, address=0x33)
#5 0x00000001ad576390 in -[NSManagedObjectContext(_NSInternalAdditions) _forgetObject:propagateToObjectStore:removeFromRegistry:] ()
Thread 3: EXC_BAD_ACCESS (code=1, address=0x33)
#5 0x00000001ad576390 in -[NSManagedObjectContext(_NSInternalAdditions) _forgetObject:propagateToObjectStore:removeFromRegistry:] ()