Hello,
 

I'm using Archer C80 in my house. The topology is:
UNO device > C80 Router > Clients

The configuration is:
PPPoE - 100mbps
Smart Connect disabled
Airtime Fairness Enabled/Disable (both tried)
2.4 GHz g/b/n with one SSID, set to 40 MHz channel 6
5 GHz a/n/ac with one SSID, set to auth width & channel auto

WPA/WPA2-Personal, AES
MU-MIMO enabled
NAT Boost enabled
QoS disabled

Whenever I connect more then 2 devices along with the Mi Tv, the router become unresponsive at that time it will take too much time to load the routers login page on 192.168.0.1. 

My device List:

1. iPhone 8
This client is connected to 5 GHz SSID
 

2. iPhone 8
This client is connected to 2 GHz SSID

3. Vivo V17 Pro
This client is connected to 2 GHz SSID

4. Vivo V11 Pro
This client is connected to 2 GHz SSID

5. MiTV - 4A Pro
This client is connected to 2 GHz SSID

6. Dell Laptop (Latitude 3480)
This client is connected to 2 GHz SSID
 

I am unable to play 1080p video smoothly on any of 3 devices simultaneously. If I play a 1080 video in any of the device then I am unable to browse the internet smoothly. 

What I have tried:
- Reset the router
- Factory reset the router

Still to serve 5-6 clients, I have to restart this router after every 2 hours.
 
Please provide any solution for this. I bought this router from Amazon on 22 March 2021