So your issue may be there. If your user log in with email password and after you are trying to add the user-agent to this logged in user, you may face some issue. Technically, Bubble replace auth of this user with the data from oAuth2, but I guess that is user log in again with email and password, this may void the oAuth2 data and Bubble will not refresh it. You could also have a bug if the user token is not refreshed if the user stay logged in with the oAuth provider but the user was created with email/password Bubble native auth. Do test: log out and log in with social network with a new account and check if you are facing the same issue.
If you want to keep the email/password Bubble auth, you will need instead to use the manual oauth2 process like described here: https://forum.bubble.io/t/showcase-manual-oauth2-token-integration/79988/