You are suggested to report the problem here with your network topology. http://ticket.tp-link.com/index.php?/Tickets/Submit The firmware version is up to date, right?

Portal Authentication. WDS can extend Wi-Fi but it may not be able to pass through it. There are many devices which can extend Wi-Fi signal but the hotspot Wi-Fi environment is more complicated than...

In picture 1, Wi-Fi is connected to modem/router's Wi-Fi or C5's Wi-Fi? Can you turn off modem/router first? And then check ethernet IP and wireless IP obtained from C5. 169.254... is an invalid IP...

As ankhazam said in #10, the bug has been fixed. No worries.

Of course we can disable WPS. You didn't see that the new firmware has fixed the issue. Upgrade the latest firmware directly if you want to protect the router.

Reset won't help? What kinds of strange IP? 169...? If you assign a static IP as 192.168.0.100 and subnet 255.255.255.0, can you login 192.168.0.1? Just connect the PC to one of LAN ports of C5...