@Elfordwp 

When adding a wireless powerline adapter to a network, even when using the same SSID you are adding a 2nd AP.  When you do use the same network credentials what could be happening is your device may be hoping between both APs, the PLC and the host router.  What I would recommend to confirm this is configure the SSID on the PLC different than the router.  Then connect to it and see if it stays stable.