pfSense

I'm running a CARP setup with two routers IPv6 only.
I don't know what the exact behaviour should be but when both routers are switched on and on both radvd is enabled in "unmanaged" mode, my clients primarily use the backup router.
This results in dropped packets at the master router which is not aware of the state, since state-sync is uni-directional from master to slave AFAIK and not the other way around.

https://forum.pfsense.org/index.php?topic=89325.0

I tried to work around this by switching from "unmanaged" to "disabled" at the slave router.
Thus the slave is still sending router advertisements and "AdvSendAdvert on" is still set in /var/etc/radvd.cfg

Hope I could be of help.