I have an HD-H250LAN which has started randomly disconnecting from the network, sometimes after only a few minutes, sometimes after an hour or two. Removing the LAN cable and reconnecting usually (but not always) fixes it, for a short while.
I thought the cable might be faulty, but I've swapped that out to no effect, and I also tried a different port on my router, to no effect.
However, I think I've now fixed it.... My model has a LAN cable cross-over switch on the back of it (later models do not, I believe). I think this switch might have got some dirt/dust in it, so I switched it back and forth a few times, to clean the contacts on the switch, and now it all seems to be ok!