Powerline 500 stopped working all connected and all lights on

Powerline 500 XAV 5421 not working, and not showing up on device settings. All 3 lights and Ethernet light remain solid green. Main router works fine. Not plugged into extension lead. Have tried resetting and moving plugs. Switched cable ports on main router.  Any suggestions as to what I may be doing wrong with this please?

My set up is Router. Cable from router port to first plug in wall socket. 2nd plug in further room (on same wiring) ethernet cable is plugged to Netgear router - as booster. All was working fine for a few months. No change to any set up. No inclement weather. No power cuts.