Thanks a lot for pointing this out to me! After I did
service uhttpd stop
service nginx start
I was able to open the standard gl.inet admin page via https://192.168.8.1 but, weirdly, http://192.168.8.1 is still adding /cgi-bin/luci automatically and I can't open gl.inet page via http. Also I am wondering what app could change nginx to uhttpd and how to get back default config of that settings without resetting the router?