On 11 Oct 2021 at 08:18p, Tommi Koivula pondered and said...
 
 TK> If you think the problem is in UFW, you can turn it off for a while. I
 TK> think the problem is not there.

Yep turned it off and problem remains :(

 TK> I think your problem is somehere in your router PI, you should open ports
 TK> 24554-24555 there as well. But as I'm no linux expert, I dont think I
 TK> can help much more.

So look at the Raspberry Pi that acts as the end point of the tunnel?

The main router connected to the internet does have 24554-24555 open already, and IPv4 traffic coming in via my ISP works OK

 TK> Your tunnel is working ok as you can poll out by ipv6.

True

--- Mystic BBS v1.12 A47 2021/09/29 (Linux/64)