Sounds like a v28 webhook regression, seen this pattern before after major upgrades.
First thing to check, API permissions on the user or application that owns the subscriptions. After upgrade, indirect permissions on some entities sometimes drop, and only /items keeps working because it sits in a different permission set. Re-check the permission set on Sales Order, Sales Invoice, Sales Credit Memo and Purchase Order.
Second, the notificationUrl handshake. BC re-validates the endpoint on subscription, and if it fails on some entities but not others, you get exactly this picture.
Third, in v28 some API endpoints had small changes. If the subscriptions point to v2.0 standard API, usually fine, but custom or beta API pages can silently break the binding.
Quick test, recreate one subscription through Postman and watch the response, then check telemetry in App Insights. Failed deliveries show up there with a clear error and close the case in five minutes.
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Regards
Gregory Mavrogeorgis
