Sudden Increase of Hard Bounce with privaterelay emails

We have been sending emails through Sparkpost via Braze inc. to the Apple Private Relay users with "@privaterelay.appleid.com" starting from around June 20th or so.

Upon August 9th 06:00 UTC, we have noticed a sudden increase of "Hard Bounce" for nearly 20,000 users using the Apple's private relay email address, rendering the email sending useless for these customers.

We have been constantly been able to send them emails, including just before this timeframe (e.g. August 9th 03:00 UTC), so it was a very sudden purge of the user data that has been done without our consent.

From a business perspective, this hurts a lot for the un-sendable users since we have no way of contacting them if not for the private address.

We are desperate to know what has happened for these customers that has been "hard bounced". We are suspecting that it should be tied to the private email and the users primary email (or user data's) tie in the Apple server being gone, but not sure enough since there is no such documentation nor any way to acknowledge what has happened anywhere.

We will provide any information possible for resolving.

Thank you.