try a different cable and other ports on your modem, if possible. You can troubleshooting like this way, connect wan port of it to another computer and if it still says wan port unplugged, which...

have you tried firmware upgrade and reset? this is very wired, you can also submit a ticket to tp-link support so they can test it.

hi AquaJedi, have you contacted the shop to replace it?

make sure remote PC firewall is off and allow devices in the same subnet to ping it.

it seems that this router can only handle that size, you contact tp-link support and maybe they will test it to confirm that.

not heard of it