You have not provided much detail for us to work with. Would I be correct in assuming that these tunnels are VPN tunnels? Based on the description of the problem that you give us I would guess that ping is not configured as interesting traffic in the access list controlling VPN on the first tunnel and ping is configured as interesting traffic in the access list controlling VPN on the second tunnel.
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...