I've tried connecting a certain IoT Hub's connection/disconnection events to a Storage Queue using the IoT Hub -> Events -> + Event Subscription, but no events or errors are ever received. The Events blade shows neither events nor errors. An Event Hub which receives these events via Diagnostics is working correctly, and I have checked that Event Grid subscription also doesn't work when Diagnostics is disabled.
I have tried two different IoT Hubs with the same and different Queue Storage and these both worked, so I suspect there is something funny about the specific IoT Hub I'm trying to set up, or some interaction with other settings which is breaking Event Grid. Is there any debugging or logging which could shed any light on this problem?