For our app, we saved a sandbox App Store Server Notifications URL with V2 enabled and independently read the configuration back. A subsequent test-notification request returned HTTP 404 / 4040007. An authenticated sandbox notification-history request shortly beforehand returned HTTP 200.
We restored the original settings after collecting diagnostics. The recorded failure is covered by Feedback Assistant report FB24885397.
What could explain this discrepancy, and what additional diagnostics would help Apple investigate?