Shipping event created from the dashboard does not call handle_shipping_event (django-oscar)

Question

I'm trying to change the shipping event type from the django oscar admin dashboard and send an email to the customer but it seems like it doesn't call the handle_shipping_event under order/processing.py

So far, I created a shipping event type and associated it with a communication event type. Then I inherited order/processing.py and add a send email function, however, it seems the shipping event created from the dashboard doesn't call handle_shipping_event under order/processing.py. I can see the shipping event written to the db.

from oscar.apps.order.processing import EventHandler as CoreEventHandler

class EventHandler(CoreEventHandler):
    def handle_shipping_event(self, order, event_type, lines,
                              line_quantities, **kwargs):

        print('It does not print this')
        # Example implementation
        self.validate_shipping_event(
            order, event_type, lines, line_quantities, **kwargs)

        # send tracking mail
        self.send_shipped_email(order)

        return self.create_shipping_event(
            order, event_type, lines, line_quantities, **kwargs)

django-oscar version: 3.1 Python 3.8.10 Thanks