I encountered same issue with my SAS5510. I googled it and found a working solution for it. I had to remove and re-add the whole SSH configuration to get the SSH access back. Still clueless about why it happened. Still looking for an explanation.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...