AUTH_USER_MODEL Model cant be "User".
For example my AUTH_USER_MODEL was "accounts.User" and django-social-auth was trying to create the user in auth_user, but changed to "accounts.AppUser" and worked.
Using User as model name works as expected, DSA doesn't try the auth_user table. Could you share your models.py? Maybe your imports were importing the User model built-in in django auth application.
AUTH_USER_MODEL Model cant be "User". For example my AUTH_USER_MODEL was "accounts.User" and django-social-auth was trying to create the user in auth_user, but changed to "accounts.AppUser" and worked.