Next time it happens, try moving a working PC to another ethernet port on the router, and if that one stops working you know its the router.

When I complained to netcomm about it they suggested a software update and then do all sorts of testing for them and reporting back. An 8 port switch and turning off wifi was easier, and it seems with only a single port on the netcomm in use it doesnt forget how to bridge between things and is reliable.