SHM lag in reporting devices joining

When I turn on my laptop and join the network, I get an immediate notification on my smartphone about a new device joining.  

Last night I joined the network at 8:30 or 9:00 PM.  And got off midnight.  I happened to notice the phone in the early hours, and it reported a device (the same as the IP address as on my laptop that evening) logged in after my logging out.