I'm trying to change uHttpd to lighttpd for now.
And also tried to follow instruction on https://openwrt.org/docs/guide-user/luci/luci.on.lighttpd which is not working. I only can see the auth page and nothing happened when I press 'submit' button.
The problem was seem that a chrome cache problem since keep change the server configuration to reload pages.
If you face the similar problem, change the web browser temporarily while testing like MS Edge.