Troubles Writing to Private Folder while Testing with TestFlight

I've developed an app that allow me to send messages to all users by entering a record in Public database. On each users device, the app takes that Public record and creates a record in their Private database to track the Read and Deleted status.

It works flawlessly on the simulator and about 1/3 of the devices enrolled in my TestFlight. The other 2/3 are unable to write to their Private database. In fact, the CKContainer.default().privateCloudDatabase.save() operation causes the app to crash if I let it run.

I've looked at every Google link and I just can't figure out why this works for 1/3 of the users, but not the other 2/3. Incidentally, the 2/3 of the group that can't save to their Private database are also unable to save their Notification Subscription.

All devices are running iOS 18.0 or better iPhone 11 through 16 in testing pool. Each portion of the working/not working group are a mix of iPhone versions.

if !found && checkIcloudStatus() {
                CKContainer.default().privateCloudDatabase.save(loadPrivateData(n: processedMessages[index].recordName)) { returnedRecord, returnedError in
                    print("Adding new message to Private and error is: \(String(describing: returnedError))")
                    DispatchQueue.main.async {
                        self.processedMessages[index].record = returnedRecord ?? CKRecord(recordType: "messages_private")
                        self.processedMessages[index].unRead = true
                        self.processedMessages[index].deleted = false
                    }
                }
            }

func loadPrivateData(n: String) -> CKRecord {
        let record = CKRecord(recordType: "messages_private")
        record["deleted"] = "false"
        record["messageId"] = n
        record["unRead"] = "true"
        return record
    }