This is the WebUi for the TL-WPA8630P unit, because only wireless PLC device has the Web UI. To view the whole TL-WPA8630PKIT, you can install the tpPLC utility on the PC and check if the 2 units are...

When the PC is connected to the WR841N router, what is the gateway on the PC, it's 92.168.0.1 or 192.168.1.1? Sometimes, if router detects there is IP conflicts betweent its WAN and LAN, its LAN Ip...

Same way to downgrade as upgrade http://www.tp-link.com/en/faq-688.html. Not every firmware versions you can downgrade to, it depends.

I would say contact tplink support to get a solution

Can you access the C7 with its IP address? like http://192.168.0.11?

What if you tap the plug on the Kasa app to turn it off and on? Would it respond immediately? If yes, the issue might be with the Google Home