Query returns None in Celery tasks

I have a celery tasks in my application but when I try to query the database in the functions, some of them returns Does not exist or None

@shared_task
def email_on_assign_reviewer(submission, reviewerlist):
    """
    Send an email to the Reviewer when they are assigned to review
    """
    print(submission)   # prints normally
    print(reviewerlist) # this prints the list of id of reviewers perfectly  
    submission = Submission.objects.get(id=submission)
    print(submission)  # this prints the submission perfectly  
    
    context = {"some": "context"}
    
    for id in reviewerlist:
        reviewer = Reviewer.objects.filter(id=id).first()
        print(reviewer)  #this returns none 
        if reviewer:
            context['reviewer_name'] = reviewer.user.first_name
            utils.sendEmail(
                context,
                template="review_assign.html",
                to=[reviewer.user.email]
            )

MY VIEW

    def perform_create(self, serializer):
        submission = Submission.objects.filter(id=self.kwargs['submission_pk']).first()

        *SOME LOGIC*

        data = serializer.save()
        for i in reviewerlist:
            print(Reviewer.objects.filter(id=i).first())  # this prints the reviewers perfectly 
        
        tasks.email_on_assign_reviewer.delay(submission.id, reviewerlist)

MY SERIALIZER

def create(self, validated_data):
        submission_id = self.context['submission_id']
        user_ids = validated_data.pop('user_ids', [])
        existing_profile_ids = Somequery.objects.all()
        for user_id in user_ids:
                if user_id not in existing_profile_ids:
                    reviewer = Reviewer.objects.create(submission_id=submission_id, user_id=user_id, )
                    reviewers_to_create.append(reviewer.pk)
                    
        return reviewers_to_create

In some tasks, the submission returns DoesnotExist