All traffic going through PacketShaper/AppVantage gets controlled with a policy. Unless you have changed it, ICMP inherits the default policy (priority 3). Since priority policies are first in/first out control, it is possible ICMP packets will get delayed when competing with other flows in the same priority and higher.

To prevent ICMP’s response from slowing down, either create a higher priority policy for the ICMP class or create a small partition.