I have this system existing of a total of 5 Deco M9 plus. 

The main Deco is wired directly to my cable modem. From the second port a Poe-switch is connected.

Two satellite Decos are connected to this Poe-switch. Two others are connected wirelessly.

Everything works fine for quite some time. But since a couple of weeks sometimes the main Deco fails to connect to the cable modem. The led is red then and no internet is passed through. 

I then have to reboot the main Deco in order to restore the internet connection. 

At the moment of disconnecting, the cable modem still has a stable internet connection. 

It happend multiple times already and I wonder if others experienced same issues and do possibly have an idea how to find out what happens or know how to solve.