Just looking through all this and noticed your picture of the plugs. Wifi extenders and powerline adaptors never work correctly if they are plugged into extension sockets and even worse if they are surge protection ones, as they pick up interference from the surge protector.
I had the same problem kept disconnecting and poor speeds, plugged both powerline adapters straight into the wall sockets and never had a problem since. I now have 4 powerline adapters plugged in now including a wireless one in the garage without any problems.
Hope this helps
@ifanyonecan thanks for your info my powerline adapters are all plugged into a wall socket now they have been like this since those pictures I did it straight away but I am still having problems with my connection it's always up and down never consistent