Most likely the software on the router has a problem. There are plenty of indications on the internet that this particular router has memory leaks in certain configurations. A memory leak is really misnamed, it occurs when the application uses a piece of memory and then forgets about and uses another, with the limited amount of memory on a router it soons runs out of memory even thought most of it isn't actually in use.

It sounds as though the router resets itself from time to time and that clears the problem.

To test, when you get the problem, unplug the router for 30 secs and then plug back in. Once initialised if you have a WiFi network its the router.

Solution, either check for firmware updates for the router at Belkin or switch the router off regularly, perhaps once a day, before its memory is exhausted.

Simon