After I posted my "test" in the topic, I received two PM's (almost immediately) that they received that notification but not erv's (or not as quickly as Erv's).
This sounds like a server issue. The notification is obviously working... but if the server is slow or overloaded, you can get a delay. I don't think there's much we can do about that but the Admins would know better.
Same thing with the PM notifications. Sometimes I get them instantaneously, other times... it can take an hour.