DHCPv6 address ignored on WAN

[keyser]

I have a peculiar issue with pfSense IPv6. My IPS started offering IPv6 if I send the correct IA- options. But pfSense is acting up VERY strange on me.

When I enable DHCP6 on WAN (and set LAN to track), I get the a strange packet capture sequence.
1: My box starts soliciting for DHCP6 using its WAN link local.
2: It gets two adverticements immidiately with the same offer of a fixed GUA address (and PD).
3: My box runs wanrenew6 again and solicits again from link local
4: It gets the same two advertisements with the same offer of a fixed GUA address (and PD)
5: My box does a router solicitation on ICMP with its link local
6: It gets a router advertisement from the upstream router (link local addresses)
7: My box performs Slaac to assign itself a GUA on WAN from the router advertised prefix.
8: From then on box uses the Slaac address it assigned itself to try the DNS's it recieved and communicate further with the world (with no answer)
9: Parallel to that it does another two DHCP6 solicits where it both times get the same GUA fixed IP offer
10: It eventually assigns/accepts the DHCP6 offered address to a local IO like the Slaac address but it remains unused.

The problem:

My ISP requires me to use the DHCP6 assigned address as source to get routed to the internet. So pfSense itself cannot access anything (DNS and so forth).
My pfSense also completely ignores the offered PD /48 even though i requested it, so nothing on LAN gets IPv6 addresses. There are no dhcp6c debug entries about the PD at all.

The really weird part:

After about 3 -4 hours my pfSense suddenly reassigns the DHCP6 offered address as the primary address, and then pfSense itself has Internet access over IPv6. It still ignores the PD completely. A reboot starts the process over.

Any ideas what this is about. I have yet to experience one working DHCP6 pfsense box out the 20+ boxes I manage across 4 ISPs that all offer native IPv6.
The DHCP6c module in pfSense is just a huge malfunctioning mess in my experience.

[Bob.Dig]

@keyser Name your ISP and country. It is working fine here as long it is not changing... dynamic IPv6.

[keyser]

@bob-dig This is in Denmark, and the ISP is called Kviknet.
I know My used settings at this time works with kviknet in other parts of the country (i have a friend using pfsense with kviknet), and more than One OPNsense uses them as Well.

So what things could influence this and cause My dhcp6c Client to behave so irradically?