I have used this kit for years with no issue to provide a LAN connection in my home office upstairs in my house.

Now, since i had it unplugged while i had building work done, it wont hold a consistent connection (getting either a red pair light, or no pair light and slow flash power light). If they are plugged in next to each other, or even anywhere on the ground floor they are fine but if plugged in upstairs they wont work. 

Nothing has changed apart from having a house extension built.

They used the upstairs socket ring main with a fused spur for both the lights and sockets in the extension, lights are LED down lighters and i have smart switches to control them. 

I have tried some elimination work and suspect it might be linked to the LED spot lights/ smart dimmer switch as once they have been on for a few minutes the connection drops on the powerline adapter. 

Is this possible? If so, is there a way to cure the issue without major wiring changes?