Until iOS 17.2, the didreceiveremotenotification function was executed for remote notifications without an alert key in APNs, but this is not the case starting from version 17.3.
I tested it with the same app, different versions.
Silent (aka background) notifications without an alert key have always been heavily throttled; before or after iOS 17.3.
What you are observing is not due to a change in behavior but probably due to different balancing for power efficiency, if not totally coincidental.
Silent notifications can be delayed at the server, or ignored on the device based on device conditions like power state, thermal conditions, data quotas, etc.
While you can expect 1-2 silent notifications per hour to be delivered to your app, it is entirely possible that you receive none.
This has always been the case and not new to 17.3
