Same problem here, 7month old LS421DE drops off the network often. Stays connected for a few hours and then drops off the network without any warning and has to be rebooted to connect again. Problem started after the latest fw update.
Reply from Buffalo support:
Reboot, ensure ip is set on the same network. Replace the unit (no buffalo centres in India, also not a good way to solve a problem), No official way to downgrade the fw, to reinstall the firmware must format the drives (not doing that, have nearly 6tb worth data on it)
Does anyone have any solutions for this??