In deploying a number of Cisco 2960X Switch Stacks containing between 4 and 8 members I’ve observed the following error message logged:
Failed to send hrpc non blocking message
The issue appeared after upgrading from 15.0(2)EX2 to 15.0(2)EX3 and persists through to 15.0(2)EX5. Following extensive troubleshooting both internally and with Cisco, the problem was narrowed down to the device classifier. Whenever a new MAC is learned the switch will create a new device classifier session and associate a corresponding session ID. This needs to be synchronised across all stack members. Due to issues with the device classifier the switches are unable to maintain this synchronisation.