It\'s written in the doc that:
Another limitation of custom User models is that you can’t use django.contrib.auth.get_user_model() as the sender or target
You can simply use the setting AUTH_USER_MODEL or any model as a string, e.g. 'users.MyCustomUser':
AUTH_USER_MODEL
'users.MyCustomUser'
def user_post_save_handler(**kwargs): # do something post_save.connect(user_post_save_handler, sender=settings.AUTH_USER_MODEL)