Hi @adk_edv,
I'd recommend looking at the account details to see if you can spot any differences between the newly created account and the original account that was already created. Generally if JIT is creating a new account, it would mean some required piece of information is not matching in the original account details (login id, email, sis_is come to mind, but sound be other things). We don't have google set up as an SSO provider here, but do have SAML which should function similarly. I don't have any other great advice for you right now, though if this is a small number of accounts, you could manually merge them together as a workaround.
-Chris