Hello@ddonlon,

Do you mean all the lights will go off on the one powerline unit and it stops working? it is suggested to try a different wall socket for the Lights-Off unit, it could a poor contact with a socket. Can you swap the location between 2 units and see if the issue occurs when plug in a certain socket? Please try to disable power save mode on for powerline units as well. 

https://www.tp-link.com/support/faq/2018/