Usually QOS function will just limit the speed instead of block data, is the Foronius Solar system using the APP or website? If you wait for a long time, can you see the page load?

Hi, Set up the D7 as a access point will be more suitable in your case. Then you can use the wifi from the TD-W8968 and Archer D7. Change the D7's LAN IP address to the same subnet with the 8968,...

If the Deco still working when the light turns to red, you can try to change the DNS server to 8.8.8.8 and 8.8.4.4, may it help.

Yes is port 80.

press the pair button on the adapters for 15 seconds then repair them, it may help..

powerline device will be affacted by the electric power environmental, you can check whether there are any high-power electrical appliance running at night, and try to move the device away from them....