IPv6 routing, Verizon FiOS, dhcpcd

Good day.  This is picking up after a long thread a couple weeks back:

Subject: IPv6 networking problems in 14.3
Archive: https://lists.freebsd.org/archives/freebsd-net/2025-September/007532.html

So following Tom Pusateri’s suggestion, I pulled an old server out of the
rack, and set it up near the center of the house.  From here, I could
disconnect everything and plug directly into the ethernet out to the Verizon
ONT.  I’m running with a simplified rc.conf, and mostly the same dhcpcd.conf
as my real router.  I am not using pf at all, nor most of the other services
the router uses.  Just system DHCP from Verizon 'ifconfig_bce1=“SYNCDHCP”'
and dhcpcd.  (Well, +ssh, +zfs, +ntpd, but…)

Lots and lots of testing showed me:

1. 14.1 and 14.3 seem to act the same
2. If dhcpcd starts up before the interface has a link, which it frequently
does, the Verizon LL router address is never reachable.
3. If I delay starting dhcpcd until after IPv4 connectivity is established,
dhcpcd sets up the same way, but the router LL is reachable, and IPv6
routing works.

There are a couple issues here that complicate things.  First, I’m using
dhcpcd for IPv6 only, which means delaying startup is fine.  But, if
someone were using it for general networking, that’s clearly a blocker.
Second, I cannot imagine why starting dhcpcd earlier caused the kernel
to somehow become unable to reach the ISP v6 LL address for the router.
If dhcpcd can’t talk to anything, it backs of and tries later.  When it
tries later, it gets DHCP6 responses, and does what it should do. 
However, the LL address that it gets from the RA just isn’t reachable.
“ndp -an” shows it as “(incomplete)” for a second, then not at all.

So, first, why if dhcpcd starts early does the system get into a state
where it is unable to reach the advertised IPv6 router?  And that this
won’t ever fix itself.  (2+ hours tested on test box, days/weeks seen
on original router)

                - Chris