It sounds like you might be encountering this issue: Integrity error during social login: duplicate key violates unique constraint on user table · Issue #3266 · pennersr/django-allauth · GitHub.
A workaround is to use one of the suggested fixes in your own signup form. E.g.
class CustomSocialSignupForm(SocialSignupForm):
"""Custom social signup form to work around this issue:
https://github.com/pennersr/django-allauth/issues/3266"""
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
self.prevent_enumeration = False
Then in settings.py
SOCIALACCOUNT_FORMS = {
"signup": "apps.users.forms.CustomSocialSignupForm",
}