On 13 Oct 2021 at 09:34a, Paul Hayton pondered and said...
 
 PH> If I can ping to the box that's not enough to know things are OK right?
 PH> OK will see what I can find.

I think I figured it out (at last).

It turns out the Rpi endpoint of my he.net tunnel was missing some FORWARD rules in the ip6tables setting. When I finally dug into that and saw it was missing such a rule for the new static IPv6 I had set for my new Linux box things finally started working.

If you would like to test 

agency.bbs.nz
ipv6.agency.bbs.nz

ports 24554-24556 

I'm hoping all is well now.

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