I would suspect it is the ISP router. If you have not already tried, I would first try switching ports that the C60 is plugged into on the ISP router to see if that makes a difference.

You need to connect technical support directly to see if they have a Beta for you.

After a power failure, it takes several minutes for the modem and router to get the connected again. Please note the router and modem lights when all is working okay and then again after a power...

Try using the TP-Link's Tether app. Not sure if you can control the guest network for you model but appear I can with my Archer C8.

Try replacing the ethernet cable with a new one. Wiggle the cable and see if that causes an issue as you may have a bad connector in the PC or the router. If your PC can connect via WIFI, try that...

Okay, you have a power failure, How long do you wait to see if the connection is re-established? What do you do to reset? Could it be that your modem or ISP that is taking a long time to reset?