Great! I’m fairly sure that it’s the mismatched emails that are causing the problem, not the ‘Create Discourse User on Login’ setting. All it’s doing is initiating the login process.
I’m surprised that this hasn’t come up before. The easiest solution might be to delete the admin1 user on Discourse and then edit your email address on either Discourse or WordPress so that the email address for both admin accounts match. Then re-enable SSO and try again.
If you don’t want to edit your email addresses, a temporary solution would be to create a new user on your WordPress site using your Discourse email address and then use that WordPress account to log into your Discourse admin account.