There are several bugs that can cause this problem, including CSCtg0692 and CSCtc37947. I would suggest an upgrade to 6.3.1172.3 to get around these issues and that should take care of the problem. Here is the upgrade guide:
Login to the FXOS chassis manager.
Direct your browser to https://hostname/, and log-in using the user-name and password.
Go to Help > About and check the current version:
Check the current version availa...
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...