@David-TP Hi, thank you very much for your reply. 

No, when the second deco losses connection, it means that sometimes the light turns red, and sometimes it stays green but the devices connected to this second unit losses internet (connected to the second deco either via WIFI or the single ETHERNET free port).

That's why i believe it has something to do with the IP management of the switch which does something either to de second DECO unit or, to the devices connected to it. 

Although the second Deco unit is at WIFI range from the first one (i tried un-cable them, it has half signal) when the Ethernet backhaul does this problem it never switched automatically to WiFi backhaul, so i think it detects the Ethernet cable just fine. 

I believe the cable works because i have the the device that test the cables and also, when I remove the switch and connect both deco units directly with the same cable the problem is gone.

I have the switch for about 2 weeks and almost every day this problem happened, and when I removed it and connected the decos directly between each other for about a month and this problem never happened. 

All the rest of connection is the same, the only difference is when i put the switch between them.I would like to have some additional Ethernet ports where I have the main deco unit because its where i have my PC and PS5 that now are connected via WiFi.

Also, when the switch was placed, the devices connected via WiFi to the main deco and the PC and PS5 connected via Ethernet to the switch never lost connection, only the second deco and the devices connected to this second unit.

I have some to little knowledge in network configuration but i saw that the router has some kind of interface to administrate it and do some things to the IPs designation. 

Thank you for your time

Best regards