Your Heart becomes unavailable on your LAN after approximatly a day. You can't reach it through the app and it doesn't show in your WiFi device list either.
Know affected routers
This problem has been seen on the above routers and it has to do with the lease time in those routers. When the lease time has expired the Heart is dropped from the network and are not allowed to reconnect. Try chaning the Lease Time to see if has an affect and update to the latest router firmware.