@Kevin_Z 

Hi, how are you? 

Thank you for the fast response!

Below my answers:

1. What is the led status of the Archer C5400 when it stops working?

All normal from the front panel, any problem with the LEDs notifications at the unit

2. Try to log into the web UI of the Archer C5400 and take a screenshot of the status page and send it to us when C5400 stops working. 

The UI is normal no issues with it, the only wrong thing is that when I'm trying to access I have an extremely low response accessing it.

3. In the meantime, please connect your computer to the modem directly and verify whether you can access internet; if so, please connect the computer back to the C5400 by wired cable and log into the web UI to clone the MAC address. 

Yes, I do that I have my network now working without any issues I remove the TP-Link from the middle and I'm using the ISP Router as my main WIFI Access point now working without issues for about a week, the internet connection is reliable with great bandwidth and stability, no connections interruptions all working as expected.

4. Besides, how do you make it work after it crashes down?

The device it is not crashing is offering an unstable connection to the internet sometimes is working OK sometimes is not working, my experience is that using the C5400 I have an intermittent internet service no matter if it is WIFI or using an Ethernet Cable all the LAN communication is working perfectly well. I disabled all the security features thinking that is consuming additional resources in the device but nothing changes. Any suggestion?