I installed my Archer C9 router on January 20, 2019 and it worked fine for over a year then it started dropping the internet access.
I would have to turn my Archer C9 router and my modem (Netgear MR1100 Hotspot) off and back on to regain my internet access. Sometimes this would happen multiple times a day.
I found this link in a Google Search
Archer C9 keeps disconnecting
A TP-LINK tech named Josh had me change the Primary DNS
This change worked for a week and then my internet access started dropping again.
Amazon gave me an Archer A9 to replace my Archer C9 which has been discontinued. The same problem happened.
At that point I thought my TP-LINK routers were not communicating with my Netgear Modem (MR100 Hotspot)
So I ordered a NETGEAR Nighthawk Smart WiFi (R6900P) from Amazon. The same problem happened.
At this point I've ruled out the TP-LINK Routers being the problem.
So I went back to my Archer C9 router.
The next step was to troubleshoot the Netgear Modem (MR100 Hotspot)
Step 1. When the Archer C9 router dropped the internet access, I turned the Modem off and unplugged the Ethernet Cable from the C9 router and plugged it directly into my laptop. I turned the Modem back on and I had internet access.
Step 2. When the Archer C9 router dropped the internet access, I kept the Modem on and unplugged the Ethernet Cable from the C9 router and plugged it directly into my laptop. I did not have internet access.
At this point I've narrowed it down to something is causing the Modem to drop the internet access.
I live in a rural area and I have one neighbor that has the same Modem and Archer C9 router as me and he has the same problem.
I have another neighbor that has the same Modem as me but has a Netgear router and he does not have a problem.
We've already ruled out it's not the Router causing the problem.
The first neighbor's wife mentioned the problem to an IT person where she works.
He told her to check if the Modem is plugged into a surge protector which can sometimes cause a low power to the Modem which can cause the Modem to drop the internet access.
The one neighbor who was not having a problem, his Modem and Router were plugged into wall outlets.
The two of us that were dropping our internet access, our Modems were plugged into old Surge Protectors which we have since replaced with new surge protectors and we are no longer have the problem of dropping our internet access.
Hope this will eliminate others from having to go through the days & months of frustrations that I've been through.