I port forward to two devices that are on 24/7 - Odroid XU4 and Raspberry Pi3. After a random interval it forgtets the forwarding. I have read elsewhere this can happen if there are a large number of devices connected but the number of devices connected is usually about the same and 20 or less at any one time.
My office has the same router but the Spark version and this does not behave in the way - which leads me believe it is a firmware problem.
Any solution for this? Can it be fixed in next firmware upgrade?