We recently updated the behavior of the "Subscription Shipping Address Updated" email notification and "subscription_shipping_address_updated" event.
Earlier, the email notification and event were triggered when a new subscription is created with shipping address details present and also whenever the shipping address is updated.
From now on, they will not be triggered anymore when a new subscription is created with a shipping address. They will only be triggered if the shipping address is updated either by your customers via the portal or by you using the API and through the admin console.
For merchants who built a workflow that depended on this email notification being triggered when a new subscription was created along with a shipping address, if required, you could modify the "Subscription Created" email template to include the shipping address details.
API users using the "subscription_shipping_address_updated" event during sign up should use the details from the 'subscription_created" event. The subscription resource in the event content will contain the shipping_address node in API response.
For more details, email firstname.lastname@example.org