Resolved. This message was a part of another issue that caused the CSS to crash. We got a ondm lifetick **FAILED** message a little further down the log. In the CSS software we are running 7.4, this is a known issue:
CSCek43439 - The CSS reboots due to an ONDM Lifetick failure because the SSL module is out of buffers. When the CSS polls the flowMgrExt.mib/apFlowMgrExtSlotFlowStatsTable SNMP OIDs, the CSS incorrectly sends these SNMP requests to the SSL module and a buffer leak occurs.
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...