I'm new to OpenWrt (Wish I'd done it ages ago!) and installed dawn and luci-app-dawn on my APs. One would show DAWN in the menu bar at the top, the other not. Due to family health issues, I'm working away from home via VPN and wanted to fix things without doing a full reboot of the AP with issues. In case anyone else has this problem, the fix was super simple - install lighttpd.