@Pascal_DECO_94 

Hi

It is possible to directly connect the XE200 to the two X50s via Ethernet wire without affecting the network. Regarding Ethernet Backhaul you could refer to the following link:
https://www.tp-link.com/support/faq/1794/

If the Internet is not available on Deco network, please refer to the steps below:

1. Check the Internet status of your ISP by connecting a PC directly into your ISP Modem/Router.

2. Reboot your ISP modem and the main Deco.

3. Use a different Ethernet cable between the ISP Modem and the main Deco, or switch to another Ethernet port on the main Deco.

4. Change the DNS Server from the Deco APP >> MORE >> Internet Connection >> IPv4, your phone has to be connected to the Deco Wi-Fi network before changing DNS settings.

5. If your PC has Internet when connected into the Modem while the main Deco doesn't, a Mac Clone of your PC might help, please refer to this article for configuring Mac Clone on Deco: https://www.tp-link.com/support/faq/2925/

  @Pascal_DECO_94 

Hi

It is recommended that you check or replace the network port and network cable.
For log, you could refer to the following link to log in to web management to check system log:
How to log into the web-based interface of my Deco