Google Auth need to setup password for Old Atlassian account to link newly created Bitbucket account.

Scenario 1: No Atlassian Account and Bitbucket account

Creating new Bitbucket account will also set up Atlassian account with password

Scenario 2: Have Atlassian Account but don't have Bitbucket account

When creating Bitbucket account using Google auth, you will be prompted to a page to enter your email address. Once enter the email address, you will be prompted again to another page where you need to enter Atlassian account password in order to link your new created Bitbucket and Atlassian account.

You will be able to log into Atlassian account using Google Auth. However, there is no Atlassian account password configured.

Hence, you will need to perform reset password for Atlassian account (Atlassian account page) to set up a password for Atlassian account. Once this is done, you will successfully sign into Bitbucket account.