In the Enforce UI console you can see in the server events for your Network Monitors an Event code 2500 with the following similar details:
Summary: Unexpected Error Processing Message
Detail: Message chain #6 encountered an unexpected error processing a message. See log for details.
This issue can occur for different reasons and so you may want to troubleshoot the issue looking at all aspects of your environment:
1. The issue might occur due to an increased amount or overload of network traffic put on your Network Monitor, in which case you should analyze your network traffic.
2. The issue might occur due to lack of disk space on the Network Monitor. You should ensure your Network Monitors do meet at least the minimum System Requirements. Please see your System Requirements Guide for details.