Same issue, 5Ghz is not visible on any of my devices, called TP-LINK and got the firmware on this issue, resolved now. You can call them and have a try.

Have you tried to clone the MAC address from your desktop? Or clone the MAC address of the E2500 router to C7. Call the 24*7 hotline may help you with that(18662258139)

Disconecting the C2600 from everything, except the power cord and a laptop via an Ethernet cable, reboot the router and also make sure the laptop is only connected to the C2600, on other network...

The stime setting of parental control really make people cofused. It's called "Internet access time", however, it real meaning is during the highlighted green time period, the filtering rule takes...

Deco doesn't support the VLAN tag, you can setup the deco system in AP mode and connect it to a router that supports VLAN tag.

How often does it happen? Are you too far away from the Deco unit that the signal is not stable? And how many devices connected to the Deco network at the same time? The galaxy S6 phones are at the...