@Mr.Tskap 

You could swap that unit either with another satellite to see if it follows the node. If the issue stays at the kitchen, it might be the connection from the kitchen all the way to where it goes (switch?) so maybe the cable/port/switch port may be the issue.

@Mr.Tskap did you ever sort this as mines just started the same issue? Regards

@LawrenceB The issue turned out to be a problem call "backlogging" or something similar (it has been awhile). This is a know problem (there are support articles on the tp-link website) where even though the M5's are hard wired together, they form a "loop" that becomes unstable and this is why my one unit would occasionally blink red as it was randomly getting dropped from the network. I solved the problem by setting up the kitchen unit via wi-fi (I was able tp p/u a strong enough wi fi signal from the main unit) instead of ethernet. So instead of etherneting two units off of the main (like I originally did when I had the problem), I made one connection ethernet and the other connection from the main unit wi-fi. From these two units, I then used ethenet connections to Deco #3 and #4. Hope this helps.