@HK77 

The Solution (Worked In Our Case)

Update the firmware to the latest US version. If you are not from US, you may not have one for your country. So you have nothing to do except flash US firmware. Your router will warn you about incorrect region but don’t be afraid to flash it.

1. Go to the Archer C7 web page on TP-Link support website for United States. //www.tp-link.com/us/download/Archer-C7_V2.html#Firmware
2. Download the firmware Archer C7(US)_V2_170525 with published date: 2017-07-24.
3. Log in to your router’s config (192.168.0.1 by default if you haven’t changed its IP-address).
4. Head to System Tools > Firmware Upgrade.
5. Click Choose file: 
6. Browse the firmware file and click Open: 
7. Click Upgrade: 
8. Wait until device reboots.

Once we installed the US firmware our Archer C7 stopped dropping 5 GHz Wi-Fi and losing the Internet connection. Now it is working like a charm during 2 months without reset.

The Workaround: Disable Hardware NAT to Fix Archer C7 Hangings

1. Log in to the web interface.
2. Go to NAT.
3. Disable Current Hardware NAT Status.
4. Click Save: 

Please, let us know if this helped you stop your TP-Link Archer router hanging.

Thus, we must admit that Archer C7 is nevertheless a great router (again) with stable Wi-Fi and gigabit LAN and WAN ports. We hope that TP-Link won’t make such lapses with firmware in future. We’d like to remember you that this story was about Archer C7 with hardware version V2.