Firmware v2.0 is very different from v3.0 in web architecture.

I have a question: Did you ever ever have any 3.x firmware running with UI? If not then this is the problem:

You should not access 192.168.8.1/index.html. It will redirect you to luci which does not exist. The correct index file is not index.html

So you need to clear your browser cache or use private window and access 192.168.8.1, not 192.168.8.1/index.html