Powerline 1200 Pick a Plug Blinks

Try putting them on the same circuit. With home circuits all being wired back to a breaker box, them being 40 ft away could actual mean they're 100+ft apart depending on how the wiring is setup. 

And not all homes work well with powerline. Many things impact it such as: 

gfci outlets

surge protectors

arc fault breakers

high draw appliances/devices

cheap/old/bad/going bad electronics

even cell phone chargers

old or bad wiring

These things can all add interference to the powerline system. So try them on the same electrical circuit and see if they work. If they do, its probably something adding interference as the further apart they are, the more issues it creates. But even if it still happens, doesn't mean it isn't something adding interference. It just means that device is adding so much, its even overwhelming individual circuits.