Policy Trace and Packet Capture are needed to get a full picture of traffic-related issues. (This supporting data is required for a Service Request)
How to use policy trace to debug access issues
Using packet captures - Quick start guide
Upload sysinfo, event logs, and other required files to case
How to send service information from a ProxySG to Symantec Network Protection to update a Service Request?
The below techniques can be used to identify slow or failing URLs for use in data collection filters.
Other related solutions: