Cycle detected in CKModifyRecordsOperation when trying to bulk save

I'm working to refactor a somewhat clunky iterative save loop for CloudKit to use CKModifyRecordsOperation and bulk save records.

I have a Course, which has 1+ Weeks, each which has 1+ Lessons. Previously I'd create the Course in CloudKit, then create the Weeks, then the Lessons and circle back to update the Weeks with the Lesson references once created. And also fetch and save the Course record with the references to the Weeks once Weeks were created.

I've refactored to create all (Course, Week and Lesson) records locally, with the relevant references set up. E.g., course["weeks"] contains the record references for each week I've created locally, for example:

Code Block 
course["weeks"] = getWeekRefsForCourse(for: allWeeks)
func getWeekRefsForCourse(for allWeeks: [CKRecord]) -> [CKRecord.Reference] {
		var weekRefsArray: [CKRecord.Reference] = []
		for each in allWeeks {
			let weekRef = CKRecord.Reference(record: each, action: .deleteSelf)										 
			weekRefsArray.append(weekRef)
			return weekRefsArray
}

The issue is when I go to save, the error I get back is:

Invalid list of records: Cycle detected in record graph

This suggests that I've got a record referring to itself, but I've gone record by record and I I can't see anything. The Weeks reference the Course and the Lessons, but not themselves, etc. So my only theory is that because I'm trying to save items that refer to other items that haven't yet been created, what I'm trying to do isn't possible.

Is the correct protocol here actually my original approach?

Or is there something I'm missing?

Original approach:

1. Save Course

2. Save Week

3. Save Lessons

4. Update Weeks with Lesson references

5. Update Course with Week references

CKModifyRecordsOperation code:

Code Block 
    let bulkSaveQueryOp = CKModifyRecordsOperation()
    bulkSaveQueryOp.recordsToSave = [courseRecord]
    bulkSaveQueryOp.recordsToSave?.append(contentsOf: weeks)
    bulkSaveQueryOp.recordsToSave?.append(contentsOf: lessons)
    //note I've confirmed I have the correct number of records
    bulkSaveQueryOp.modifyRecordsCompletionBlock = { records, recordIDs, error in
    if let error = error as? CKError {
          log.error(error)
       } else { // success }
    }
    CKContainer.default().publicCloudDatabase.add(bulkSaveQueryOp)