The causes are one or more of the following:
- Connection halt during ClusterXL failover - services that are not synchronized on the cluster.
- Security Policy install occasionally causes ClusterXL failover - and if connections are not set to keep data or rematch, they are interrupted.
- Aggressive aging kicking in on a highly loaded gateway / cluster.
- The traffic is non-TCP RFC compliant.
- SmartLog shows that traffic is being dropped as "TCP packet out of state: First packet isn't SYN"
- Session has been expired.