You can reset and re-configure your powerline adapters to give a try.

You can try to plug your new TL-PA211 at some other place to see if the speed is always so poor. If not always so, then it must be the electric noise which caused your problem. If always so, then...

You can log into the management webpage of TL-WPA4220 via utility. Here is the link of this utility: http://www.tp-link.com/en/support/download/?model=TL-WPA4220&version=V1#tbl_b

This link will help configure your powerline adapters: http://forum.tp-link.com/showthread.php?75985-How-to-build-a-secured-powerline-network&region=china

TL-LINK powerline adapters actually check the physically connectivity to decide whether it should go into PowerSave mode. So if your router is always power on, then your powerline adapter will not go...

I guess maybe the electric noise caused your problem. At different positions, there will be different electric noises, and maybe the electric noise is much heavier at the new position.