Connecting over powerline and wifi

Solution 1:

The issue here is likely you have inadvertently created two unique subnets that cannot communicate between each other because there is a router in the middle of everything.

Most routers you can disable DHCP and just connect everything to the LAN ports, but you will have to make sure the LAN IP of the device does not exist in the current network. Some routers, like this TP-Link as you discovered, has the ability to operate in a special mode like repeater or bridged device that allow it to essentially act as a switch, passing through the existing network rather than segregating it.