SwiftData does not persist change on relationship on iOS 18 beta 7

I came across of something I'm struggling to comprehend. I've got an iOS app based on SwiftUI and SwiftData + CloudKit. I wrote it using Xcode 15 and the target was iOS 17. Everything works fine in this environment, but after upgrading my phone to iOS 18 beta 7 something very strange started to happen with SwiftData on a physical device and in the simulator.

Every time when data is updated, to be precise - when the relationship is modified, the change is reverted after 15 seconds!

I've got the following settings on and nothing can be seen it's going on there in the logs

• -com.apple.CoreData.Logging.stderr 1
• -com.apple.CoreData.CloudKitDebug 1
• -com.apple.CoreData.SQLDebug 1
• -com.apple.CoreData.ConcurrencyDebug 1

Here you are some simplified code extraction:

@Model
final public class Note: Identifiable, Hashable
{
    public private(set) var uuid = UUID().uuidString
    var notification: Notification?
    ...
}

@Model
final public class Notification: Identifiable, Hashable
{
    var dateId: String = ""
    @Relationship(deleteRule: .nullify, inverse: \Note.notification) var notes: [Note]?

    init(_ dateId: String) {
        self.dateId = dateId
    }
}

@ModelActor
final public actor DataModelActor : DataModel
{
    public func updateNotification(oldDate: Date, newDate: Date? = nil, persistentModelId: PersistentIdentifier) {
        if let note = modelContext.model(for: persistentModelId) as? Note {
            updateNotification(oldDate: oldDate, newDate: newDate, note: note)
        }
        try? self.modelContext.save()
    }

    private func updateNotification(oldDate: Date? = nil, newDate: Date? = nil, note: Note) {
        if let oldDate = oldDate {
            let notifications = fetchNotifications()
            let oldDateId = NotificationDateFactory.getId(from: oldDate)
            // removing the note from the collection related to oldDate
            if let notification = notifications.first(where: { $0.dateId == oldDateId }) {
                if let notificationNotes = notification.notes {
                    if let notificationNoteIndex = notification.notes!.firstIndex(of: note) {
                         notification.notes!.remove(at: notificationNoteIndex)
                    }
                    if notification.notes == nil || notification.notes!.isEmpty {
                        self.modelContext.delete(notification)
                    }
                }
            }
        }
        if let newDate = newDate, newDate > Calendar.current.startOfToday() {
            // adding to a new collection related to newDate
            let notifications = fetchNotifications()
            let newDateId = NotificationDateFactory.getId(from: newDate)
            if let notification = notifications.first(where: { $0.dateId == newDateId }) {
                note.notification = notification
            } else {
                let notification = Notification(newDateId)
                note.notification = notification
            }
        }
    }
}

Spreading save method here and there does not help :(

I've used Core Data Lab software to look into database and I can clearly see data changes are reverted for relationship property.

Example:

In Notification database there is one element:

2024-08-26 (3)

with 3 notes attached. I modified one note to send notification on 2024-08-27. Changes in database reflects situation correctly showing:

• 2014-08-26 (2)
• 2024-08-27 (1)

BUT!!! After 15 seconds doing noting database looks like this:

• 2024-08-26 (3)
• 2024-08-27 (0)

All changes were reverted and all notes are still attached to the same date as they were at the first place.

Any thoughts?