There are two NAT on the TP-LINK menu.One is software NAT, another is Hardware NAT. Disable Hardware NAT will not effect the port forwarding function or any other NAT function

Are you using the Window 8 version for the usb printer controller? http://www.tp-link.com/en/support/download/?model=TL-WDR4300&version=V1#tbl_b Check if there is any third-party anti-virus software...

How about give a try to turn off the Hardware NAT on the router?

Hi, Olivier! Channel 8 is not a stable channel as far as i know. How about change the channel to 1/6/11? Sometimes disable the hardware NAT can also be a good try.

Go ahead and do the reset by the web interface.What is more, you can also try to disable the Hardware NAT. On the TP-LINK page, go to NAT-->Disable the current hardware NAT-->Save.

How about give a update to the TL-WDR4300 firmware？Go to the TP-Link official website to get it and upgrade.