Asus router and Virgin V6 box issue

[CSK423]

I currently have the superhub 3 in modem mode with Asus ac86u router. All works and at the speed it should except for the connection between the V6 boxes ie playing a recording from another box.

3 no. V6 boxes

box 1 hardwired into the router
box 2 hardwired into the router
box 3 hardwired from router to powerline and powerline into V6 box.

Only box 3 will connect to box 2. There is no other connectivity between any other box in or out. They are visible but won't play any recordings.

Thoughts ?