The TP-Link Archer C6 is a cheap and overall reliable 2.4 and 5 GHz WiFi Router, but the firmware version 1.3.0 has a major flaw:
After a few hours all connected 2.4 GHz devices are dropped and not able to re-connect, although the 2.4 GHz WiFi is visible to all devices all the time. The only way to solve the problem is to reboot the Archer C6. The 5 GHz WiFi seems to be not affected, but as most smart home devices have 2.4 GHz WiFi only, the whole smart home becomes a dumb home through TP-Links crappy firmware. Besides that, the mesh technology is activated with version 1.3.x on both bands and two hidden WiFis are created, whether you want to use the mesh feature or not. The user is not able to deactivate it.

Countless owners of the Archer C6 have these problems since April 2020 and TP-Link seems to do nothing about it. Beta versions of the firmware with version numbers 1.3.x are available, but no user ever confirmed they solve the 2.4 GHz problems. A downgrade of the firmware 1.3.x is not possible, as stated on the TP-Link website:

This FW has added some new features, it cannot be downgraded to former release once upgraded to this one.

Once you were stupid enough to upgrade the firmware through the routers webinterface, you are ruined. The router simple does not let you install older versions of the firmware. This is even true for the firmware upgrade method of loading a binary file to the router via an tftp connection via ethernet. I’ve tried this about 5 times, but the Archer C6 didn’t install the firmware version 1.2.1 over the version 1.3.0.

The only way I was able to solve this problem, was to install an OpenWRT firmware to the Archer C6 first and then an older version of the TP-Link firmware afterwards. I used an Ubuntu laptop and an ethernet switch (see note) for this. If you run into the same problem, you might want to try the following. Important: Everything you do, you do at your own risk. By installing a non-OEM firmware, you will lose your warranty (although neither TP-Link, nor your dealer might ever notice it, if you install an official TP-Link firmware afterwards).

  • Set up an tftp server on a Ubuntu PC like mentioned here:
    https://askubuntu.com/questions/201505/how-do-i-install-and-run-a-tftp-server

  • Download the OpenWRT firmware for an Archer C6 (“Firmware OpenWrt Install URL”):
    https://openwrt.org/toh/hwdata/tp-link/tp-link_archer_c6_v2_eu

  • Rename the .bin file to ArcherC6v2_tp_recovery.bin and copy it to the tftp folder

  • Change laptop IP address to 192.168.0.66 with subnet mask 255.255.255.0, DHCP off
  • Set Link Negotiation to manual, 100 MBit/s, fullduplex

  • Connect laptop to a standalone ethernet switch (not connected to anything else)

  • Switch off Archer C6
  • Connect one of the ethernet ports (not the WAN port) to the ethernet switch
  • Push and hold the reset button
  • Switch on Archer C6
  • Hold the reset button until the WPS LED (rightmost LED) on the Archer C6 and the appropriate link LED on the switch are lit (which means, the ethernet port of the Archer C6 is up and running and connected to the switch)
  • Immediately release the reset button and wait about 2 to 3 minutes. Various LED blink and after a while the power LED and the ethernet LED should be lit. The OpenWRT firmware is installed.

Then you do exactly the same with an older version of the TP-Link Archer C6 firmware:

After the installation you have a fresh Archer C6 firmware as out of the factory. All former settings are gone and you have to set it up again, but at least the 2.4 GHz WiFi works.

Note: You might be able to install firmware to the Archer C6 without an ethernet switch, but in my case the network device of my Dell laptop was just too slow to set up a working ethernet connection to the Archer C6 after the router was switched on. The Archer C6 seems to look only a few seconds for a tftp server and if nothing is found, it simply boots the current installed firmware. So I took an ethernet switch to keep the ethernet connection of my Dell laptop alive all the time. This way, the Archer C6 was able to load the firmware from the tftp server.