2024-08-05T14:38:13 Error opnsense /usr/local/etc/rc.bootup: The command '/usr/local/bin/flock -ne /var/run/lighty-webConfigurator.pid /usr/local/sbin/lighttpd -f /var/etc/lighty-webConfigurator.conf' returned exit code '255', the output was '2024-08-05 14:38:13: (/usr/obj/usr/ports/www/lighttpd/work/lighttpd-1.4.76/src/network.c.604) bind() [fe80::7802:45ff:fe40:c66d]:4433: Can't assign requested address'
I can confirm that setting the listening interface at System: Settings: Administration to "All (recommended)" by deselecting all interfaces solves the issue. When the listening interface is set manual, even if all interfaces are selected, the above error message gets thrown and access to the web interface is not possible after reboot.
"All (recommended)" is the only supported setting. Just don't mess with it unless you know exactly what you are doing.
The setting should be hidden under "Advanced" at minimum. Also creating floating firewall rules (and disabling the anti-lockout if required on LAN) is a much better way of restricting access than messing with the listening interfaces.
The thing is - this is only really useful when you need to run something on the web GUI port on some interface(s) - e.g. OpenVPN TCP/443 on WAN, or HAProxy, but still want to keep the OPNsense GUI on the default ports for whatever reason... Just way too visible as it is now.