I am using a database with NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType) Everything works fine, I save objects, read, and delete without problems. If set "-com.apple.CoreData.ConcurrencyDebug 1" : I save the object through the PerformAndWait block - ok I do fetch - receive an object, but its properties are empty (data = fault) and it crashes. (EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)) sample code: public final class  DatabaseCore {     private let persistentContainer: NSPersistentContainer     private var backgroundContext: NSManagedObjectContext!     private let queue: DispatchQueue public init() {         self.persistentContainer = Self.createPersistentContainer()         self.queue = queue         self.queue.async {             self.backgroundContext = Self.createNewBackgroundContext(container: self.persistentContainer)         } // Private     private static func createPersistentContainer() -> NSPersistentContainer {         let model = NSManagedObjectModel(contentsOf: Bundle.module.url(forResource: "TestModel", withExtension: "momd")!)         let container = NSPersistentContainer(name: "TestModel", managedObjectModel: model)         let description = NSPersistentStoreDescription()         description.url = URL(fileURLWithPath: "/dev/null")         container.persistentStoreDescriptions = [description]         container.loadPersistentStores(completionHandler: { (storeDescription, error) in             if let error = error as NSError? {                // print error             }         })         return container     } private static func createNewBackgroundContext(container: NSPersistentContainer) -> NSManagedObjectContext {         let context = container.newBackgroundContext()         context.mergePolicy = NSOverwriteMergePolicy         context.undoManager = nil         return context     } private static func saveContext(_ context: NSManagedObjectContext) {         context.performAndWait {             if !context.hasChanges { return }             do {                 try context.save()             } catch {                 // print error             }         }     } // Public public func upsert(_ block: @escaping (NSManagedObjectContext) -> Void, completion: (() -> Void)?) {         self.queue.async {             let context: NSManagedObjectContext! = self.backgroundContext             self.backgroundContext.performAndWait {                 block(context)                 Self.saveContext(context)             }             completion?()         }     } public func fetch<ResultType: NSFetchRequestResult>(_ request: NSFetchRequest<ResultType>, completion: @escaping ([ResultType]) -> Void) {         self.queue.async {             var result: [ResultType] = []             self.backgroundContext.performAndWait {                 do {                     result = try request.execute()                 } catch let error {                     // print error                 }             }             completion(result)         }     } } I set a breakpoint to result fetch func if set  "-com.apple.CoreData.ConcurrencyDebug 1": (lldb) po record <Test: 0x7b1400030070> (entity: Test; id: 0xbb200e8d680f1045 <x-coredata://1BFC3A95-3F7D-4A23-AD20-FDF23B575D73/CDLog/p1>; data: <fault>) (lldb) po record.value error: Execution was interrupted, reason: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0). The process has been returned to the state before expression evaluation. Without  "-com.apple.CoreData.ConcurrencyDebug 1", everything works correctly, without a crash. (lldb) po record <Test: 0x7b1400028c80> (entity: Test; id: 0xb29880bd32a57757 <x-coredata://1BFC3A95-3F7D-4A23-AD20-FDF23B575D73/CDLog/p1>; data: <fault>) (lldb) po record.value 0 How can this be fixed? Thank you! =) Xcode 13.3