We have upgraded a number of X460 stacks from release 15.3.1.4 to 16.1.1. I now have a single switch that has no SNMP contact. I am aware of an issue on the forum with previous release upgrades causing a problem, but my SNMP settings look fine.
Can you verify whether the default-group and default-user is enabled as well as the defaultUserView, defaultAdminView, and defaultNotifyView subtrees are configured. The following article will provide more information:
