Ikea Tradfri hub loosing connectivity

Ikea Tradfri Zigbee controllers are known sometimes to get offline, a lot of people over inet complaining on that. In case it is rebooted, it is working. The less known thing is the network disconnect also restores availability. However, disabling/enabling port on switch does not work, because some of the devices just stops transmission over ethernet port. The thing that helps is speed changing to 10mbps and back! I have my Ikea Tradfri hubs running for several months. The server pings them and if it loses connectivity, I just change the speed of the ethernet ports -- and viola! - my Tradfri hub is back online. The other problem is when devices goes offline, I have no solution -- and I do not even know how to detect that via COAPS....