My last idea you can try Gargoyle, I have WDR4300 with this firmware and I'm very happy. Link you catch in my signature and good luck ;)

If you have latest firmware and you still have the same problem return it under warranty.

Depends on what interwall messurment you want/need?? I asked about average network traffic, because I think that much traffic causes your problems with router access. This equipment is for home...

Firmware is the latest TL-WDR3600_V1_130320 like in your post information? How much network/internet traffic you generate on your router?

Thanks for information!

By Ip address is this same symptom http://192.168.1.1