I'm working in Opnsense on a strange issue where my guest and private lans SECV IP addresses flipped. When checking bandwidth graphs, it seemed this happened after I rebooted the modem this past weekend when I lost connectivity.
After messing around with gateways and firewall rules, I got it sorted. For some reason opnsense like to route everything out WAN2, but really I want WAN2 to be the guest network. It changed recently from a 24.x.x.x IP to another 70.44.x.x IP like WAN1, just the last two octets are different. Anyway opnsense seems to always think WAN1 is down but it routes my private network out it anyway.
By screwing around I got a DHCPv6 IP on my private lan. I now have a 2606:9400:ac9f:fe96 ipv6 address on my computer. My iphone also is showing two 2606:9400:ac9f:fe96 /64 ips in addition to the usual link local fe80 one.
https://test-ipv6.com is now giving me a 10/10 for IPv6 readiness. I can ping ipv6.google.com and get a reply back from 2607:f8b0:4006:81c::200e with an average ping time of 22ms.
I don't know if this is me messing around with static routes and route overrides and gateway settings in opnsense... but I can tell you this... I didn't touch ANYTHING with ipv6. My opnsense as far as IPv6 is concerned is all out of the box settings, DHCPv6 and LAN is Track interface WAN (which I had set that up for years even when I ran pfSense).
I also tweaked my limiters to fix buffer bloat issues since I'm using two WANs from the SB8200 modem and two public IP's, one for guests and one for my private lan. I had to duplicate all the rules basically and settled on a limiter of 920 down by 94 up. I tested on both networks and they both get "A" ratings now. That one was pretty tricky. I felt like pfSense limiters worked better despite the older UI and codebase.