No IPv6 connectivity after reboot / duplicate dhcp6c processes

[lostcontrol]

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Describe the bug

For a few weeks/months, my system loses IPv6 connectivity after reboot. I noticed that I have two dhcp6c processes running concurrently on the system after boot.

root    57538  0.0  0.1  13796   2364  -  Ss   19:45   0:00.00 /usr/local/sbin/dhcp6c -c /var/etc/dhcp6c.conf -p /var/run/dhcp6c.pid -n
root    57776  0.0  0.1  13796   2372  -  Ss   19:45   0:00.00 /usr/local/sbin/dhcp6c -c /var/etc/dhcp6c.conf -p /var/run/dhcp6c.pid -n

I regain IPv6 connectivity if I kill both processes and reload the WAN interface. I'm running 25.1.3 at the moment but the problem was probably already there before 25.1.

To Reproduce

Steps to reproduce the behavior:

1. Reboot the box
2. After restart, no IPv6 connectivity
3. ps aux | grep dhcp6c shows 2 running processes
4. killall dhcp6c
5. Reload the WAN interface
6. IPv6 works fine again

Expected behavior

Only one dhcp6c process should be running I guess. IPv6 connectivity should be there right after reboot, without having to kill processes and/or reload interfaces.

Relevant log files

I'll send more logs directly to Franco per e-mail.

Additional context

Original discussion: https://www.reddit.com/r/opnsense/comments/1j8pq51/comment/mh932yq

Environment

Software version used and hardware type if relevant, e.g.:

OPNsense 25.1.3-amd64
Intel(R) Atom(TM) Processor E3930 @ 1.30GHz (2 cores, 2 threads)

No IDS/IPS, no crazy plugins, no bridge configured in OPNSense. I have VLAN on WAN because my ISP sends traffic on VLAN 10.