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

Are you using the camera control tool to record? If yes, re install the control tool. What operating system have you update your PC to anyway? Does it still work on other PC?