@Alex this is the the bug report which I mentioned earlier.
I have linked to the reply as a reference point by someone who did a lot of digging into the monitoring of ipv6 gateways. I am not sure if this is the cause of the perpetual 'pending' state but its a possibly. My theory remains its related to gateways that are not pingable.
https://redmine.pfsense.org/issues/11454#note-23--
After more digging i came across more bug reports, of which a fix was made by using the "dont wait for RA" option, no such option exists for SLAAC, but I have now moved the configuration to use DHCP6C instead since that part of pfsense has clearly had more dev attention and gateway monitoring now works on IPv6. This option does assign a internet IPv6 to the l2tp interface instead of just link local. The gateway is still not pingable (monitoring is pinging 2001:4860:4860::8844), so the issue might be that pfsense will refuse to consider it online if it only has a link local address.
I also have discovered a few things which I consider to be bugs such as vpn interfaces been brought online using link local address for the physical lan interface instead of the physical wan interface, the aaisp v6 interface is actually having both link locals added to it, but luckily the correct one is added to the routing table.
