Strange thing is sometimes I have to manually reboot the router as it completly stops responding (Wired and wireless) When it stops responding, how about status of all lights in the front panel? Can...

Can you login web interface of D7 on your Samsung phone? As the router is working with all other wireless clients, try to contact Samsung for some advice. If you don't mind, disable Wi-Fi security on...

Read the post here. It may help. http://forum.tp-link.com/showthread.php?78519-Random-fault-T4U-AC1200&p=152918&viewfull=1#post152918

Is it using smart IP or static IP? Have a check on its web interface, Network---LAN.

As I know, C9 is not designed as a multi-function router. But some other of their products have different modes.

Try to configure bandwidth control. http://www.tp-link.com/en/faq-557.html