Use M5 as the primary, E4 the single mesh node.  The mesh system worked for about 24 hrs then E4 became disconnected, solid amber light on.

Restarting E4 helped get it connected and worked for about 24 hours, then the problem recycled.

The mesh used wireless connections and did not use ethernet cable.  Devices were one room apart, about 10 meters, and 2 walls in-between.  

 Firmware versions are below: