100% I had this issue for 1-2 years :) I tough it is hardware issue or DDOS, when I'm using torrents by that time. And yesterday I start to deeply investigate why router dies. Read logs, check traffic, check usb devices, drop all services and eventually come to conntrack (part of iptable netfilter) connection manager, which kill the router by out of memory exception when too many out come connection occurs, which leads to many issues including 100% cpu, traffic slowdown, dead UPNP, dead DHCP etc etc etc. Was hard to tell at first what is wrong, router become unresponsive, even after connection out burst is over. But in the end, it was DHT. For last few days I have no issues with the router.