It seems like what you’d need here are some more testing/debugging resources from Discourse.
For example, the only way to receive a test notification is to unsubscribe/subscribe from notifications, but if that works, and you’re still suspicious that other notifications aren’t going through, what can you do?
The obvious thing to do is to have another account DM you. But if you’re not careful, the DM might arrive during the push notification delay window, and, if it does, you’d have no way of knowing whether it did. (If you could at least configure/disable the push notification time window, you could turn it off (set it to 0) and test notifications that way.)
Is it possible for even an admin to check a log to find out why a particular notification didn’t go out?