Hi there!
Welcome to the Auth0 Community and I am sorry about the late reply to your post!
It appears that whenever you sign out the user, you only sign them out of the Auth0 session but not the IdP itself. That would explain why the user logs out, their IdP session is kept and they are prompted to sign in only on the Auth0 session and being redirected to the old account when that is finalized.
I would advise you to also redirect the user to the federated logout endpoint in order to sign them out with the IdP as well. You can read more about that in our documentation.
If you have any other questions or already found the solution yourself, feel free to leave a reply or post again on the community!
Kind Regards,
Nik