@TerryP 

If there is a second outlet, plug the Wi-Fi extender to that, and see if the same lag still happens. 

If the wireless network name of the TL-WPA8630P is configured to be the same network name of the router, change it so it is not the same.

If you have a computer connected with an Ethernet cable to the 8630 to see if you still get the lag. If so, move the 8630 to the same room as the first adapter. If you still get major drops then factory default each powerline device and repair them. If you still get the drops there may be issues with the device. 

Another test to do is to steal the cable from the first powerline adapter and connect that to your computer to test.