Never Get RENEWAL Notification Type on Apple statusUpdateNotification

We've found that Apple's subscription update webook calls are rather unreliable.

Based on experience:

1. Don't count on Apple to notify you of renewals. The notification may arrive arbitrarily late (often leaving a "gap" in time), or not at all. We've resorted to retaining and retrying the original iTunes-provided receipt to revalidate renewals at the end of subscription periods --the expiration dates will change to account for the renewal.
2. Don't count on Apple to notify you of cancellations, either. Same as above, calculate subscription duration, and retry receipts at the end of a period (the expiration date will NOT be updated if the subscription is cancelled).

Generally, this involves mapping the additional transactions/in_apps that are returned with the retried receipt to the original_transaction_id --and updating the expires_at accordingly on your end.

Hope this helps!

Update: In WWDC2020 Apple announced that they add a new notification type called DID_RENEW which will be sent after any successful auto-renew. More info on that in this video, starting at around 16:00.

Original answer:

I can't find the page you linked to, however this page may shed light on the subject (emphasis by me):

The App Store attempts to charge the user account 24 hours before an auto-renewing subscription expires. If the renewal is successful, there is no server-to server notification because the auto-renewing subscription did not enter into the expired state. However, in the few cases that iTunes is unable to renew the subscription (generally there was a connection problem with the credit card server) and the auto-renewing subscription is not renewed before the expiration_date passes, the auto-renewing subscription is technically considered expired. iTunes may continue to attempt to renew the subscription. If iTunes is successful, then the RENEWAL event is sent.

Meaning, you're not supposed to receive notifications for renewals, but only for cases where the subscription became expired and only then renewed. This might be the case for sandbox renewals as well.