I have had issues signing on time to time on my Archer C8. Sometimes http://tplinklogin.net/ will fail where http://192.168.0.1/ will work or the other way around. Connect with tplinkwifi.net via...

Do you lose both the WIFI and LAN on the C60? If only WIFI, try a different channel and try powering down all the WIFI devices then up one by one to see if one of them may be causing an issue.

I have an Archer C8 and it does not. Suspect the same for yours. By using one on your device, you will also see limits that the device may have. I know you would like a pure measure of your ISP.

There are many speed tests online that you can use with Ookla (https://www.speedtest.net/) one of the go-to ones. Bypass the router and test with your PC connected directly to the Modem. Be sure to...

Maybe you could add a second router. One controls the MAC addresses and the other has the guest network.

I would reset it back to factory specs and reenter the settings. After it is working, back it up.