[Answered ]-Django custom-user error: HINT: Add or change a related_name argument to the definition for 'custom_auth.CustomUser.groups' or 'auth.User.groups'

you have to override the groups and give it a related_name

custom_groups = models.ManyToManyField(
        Group,
        related_name='custom_users',
        blank=True,
    )

add this to your custom user model

As per this answer, if you specify your AUTH_USER_MODEL in your settings.py, the clash should disappear.

# settings.py
AUTH_USER_MODEL = 'custom_auth.CustomUser'