Very strange issue... Try to reset both the router and the repeater to factory defaults first. When you reconfigure TD-W8968, just keep the main SSID and ensure it works without the repeater. Later...

Follow the guide as below to check your configuration step by step. http://www.tp-link.com/en/faq-244.html If it doesn't work, provide configuration screenshots to support team directly....

How about stauts of all lights on powerline adapters when connections drops? Can you connect iMAC directly to your Sky hub bypassing powerline adapters to test the internet connection?

The firmware of powerline adatpers like PA451 is composed of PIB and NVM. A new firmware released may not upgrade PIB and NVM simultaneously. Most of the time, either PIB or NVM is upgraded and only...

Press the pair button on PA4010 which is in the existing network. Power light will be flashing on it. And then, press Pair button on WPA4220 and its power light should be flashing as well. Wait for a...

The utility should work for both WPA4220 and WPA2220. If there is another computer, try to install the utility. If the problem continues, there is a second way to login web interface of WPA4220....