iCloud Sync Failure - "Could not decrypt bytes" Error Across Apple Notes

Device Information:

• Affected Devices: iPhone, iPad, Mac
• Service: iCloud Notes
• Apple ID: Experiencing sync issues
• Software Versions: All latest iOS 18

Issue Description: I'm experiencing synchronization issues across my Apple devices with iCloud Notes. When attempting to create or modify notes, the system consistently fails with encryption-related errors.

Specific Symptoms:

1. Unable to sync notes across devices
2. New note creation fails
3. All devices are signed into the same iCloud account
4. Error persists after multiple attempts

Technical Details:

Query Endpoint Request:

URL: https://p111-ckdatabasews.icloud.com/database/1/com.apple.notes/production/private/records/query

Response (Status: 424):
{
  "uuid": "ee8881e4-329a-4a29-9383-c32a384b8045",
  "serverErrorCode": "INTERNAL_ERROR",
  "reason": "could not decrypt bytes"
}

Lookup Endpoint Request:

URL: https://p111-ckdatabasews.icloud.com/database/1/com.apple.notes/production/private/records/lookup

Response (Status: 200):
{
  "records": [{
    "recordName": "DefaultFolder-CloudKit",
    "reason": "could not decrypt bytes",
    "serverErrorCode": "INTERNAL_ERROR"
  }]
}

Modify Endpoint Request:

URL: https://p111-ckdatabasews.icloud.com/database/1/com.apple.notes/production/private/records/modify

Response:
{
  "records": [{
    "recordName": "TrashFolder-CloudKit",
    "reason": "could not encrypt bytes",
    "serverErrorCode": "INTERNAL_ERROR"
  }]
}

Troubleshooting Steps Taken:

1. Attempted to reproduce the issue with a minimal test case (creating a new note)
2. Tested with a different Apple ID to verify the issue is specific to this account
3. The error does not occur on the test Apple ID, suggesting an account-specific encryption issue

Impact:

• Unable to create or modify notes
• Sync functionality is completely broken
• Affects all devices on this Apple ID

Request: Please investigate the encryption/decryption errors preventing normal iCloud Notes synchronization across my devices. The consistent "could not decrypt bytes" error suggests a possible issue with the account's encryption keys or CloudKit configuration. The error appears across multiple CloudKit endpoints (query, lookup, and modify), indicating a systematic issue with the account's encryption system. This is for my particular Apple ID - the same email used in this support ticket.