Some issues are easy to troubleshoot with the information presented by the proxy GUI.  Issues with external services are more difficult to troubleshoot.  External services that have an impact on how the proxy functions include:

DNS, Authentication, ICAP, and other.

This document will guide you through creating a custom snapshot to monitor these external services using the health check statistics.

The ProxySG includes 2 preconfigured snapshots but you can create custom snapshot to capture data on many different data points present on the proxy.
The following KB shows an example of creating a snapshot to monitor CPU statistics.  This can be used as a guide when creating other snapshots.

• https://support.symantec.com/en_US/article.TECH241659.html
• The target use to create the snapshot to monitor health check statistics is /health_check/statistics.
• The interval should be set to 5 to gather the information every 5 minutes.
• The maximum number to store should be set to 30.
• Check enable to enable the snapshot.
• Then you can click the view all snapshots button to see all of the snapshots including the one you just created.