Thanks @kersing for looking into this. @Brendan can you give us some insight here?
I also did some similar testing with the Kerlink IoT Base Station and it seemed that the stat messages are only sent when nodes are transmitting data and a certain period after the last transmission. I'm not entirely sure about this behavior, but you are right that whether or not the gateway sends a stat message is not necessary related to a gateway being up or down. We should also look at the last packet from this gateway (@Jorma)