A strange thing happened that could possibly be related to installing YAMon (although I only noticed it a couple of days later, so can't be sure).
When I enter router's IP in the browser, it doesn't take me to LuCI but rather it lists the index of /www. To go to LuCI now I have to type in routerIP/cgi-bin/luci/.
It's not a browser thing; I tried different browsers and even a different device.