Apologies for the delay in responding. I did get sent the notification of your post but it was languishing in my spam filter.
The server is still sending me the log files so outbound comms is working and therefore I also have the IP address. We just need to fix the inbound routing, so that may be either on the router or DynDNS.
I will be back home tonight so I'll get a good look at it then.
Last restore on the DR machine was "Last update: 2017-11-17 02:11:22"
http://noprimeleftbehind.dynv6.net/stats/
although I am still having an issue with the DynDNS automatic update
but otherwise all good there.