We are currently experiencing an issue with a one-to-one field in Django where the data was not stored after assigning a value and save call is successful without any error. This does not happen to all the records. I'd say 60% of it was not saving and 40% was saving. This only happens on our production server where there are millions of rows for Model1 and Model2 and there are so many processes ongoing. We also assign a value to other fields and call save on other parts of the process after the link_item method is called.

models.py

class Model2(models.Model):
    # Some other fields here

class Model1(models.Model):
    field1 = models.OneToOneField(Model2, on_delete=models.SET_NULL, null=True, blank=True, default=None) 
    # Some other fields here

    def link_item(self, model2_id):
        logger.info(f'Linking {self.id} to {model2_id}')
        field1 = Model2.objects.get(id=model2_id)
        self.field1 = field1
        self.save()
        logger.info(f'Field 1 was set to {self.field1}')

views.py

import module

def my_view(requests):
    model1_obj = Model1.objects.get(id=model1_id)
    result = module.another_function(model1_obj, request_data)
    return result

module.py

def another_function(model1_obj, request_data):
    logger.info(f'Request data was {request_data}')
    if request_data['status'] == 'completed':
        model1_obj.some_process() # .save() is called here after assigning a value to attribute
        model1_obj.some_process2() # .save() is also called here after assigning a value to attribute
        model1_obj.link_item(request_data['model2_id']) # Logs were shown but field1 value was not set

I can see all the logs on the server were correct but when I checked the value of the field1 sometimes it doesn't get updated with the expected value. We are using Django 4.0 and Postgres 14. Any idea why?