One of ten ESXi hosts running 5.5.0 dropped off the list of hosts for its cluster as displayed in Orion/NPM 11.5.2 (IVIM 2.1.0). It is polled fine by VMAN 6.3 with its data visible in that console. It can be added as a node to Orion and SNMP creds work but it does not return any resources when doing a list resources for the node. If I do an snmpwalk on the host from somewhere else, it shows the VMware data in the SNMP output. I compared it to another of the ten hosts and the SNMP output is equivalent in terms of content (ignoring instance differences). An IVIM resync or deleting and re-adding the node does not restore it to the cluster list. It can only be added as a node since it does not get detected through the vcenter polling. In vCenter it is operational and fully visible in the cluster. After being added as a node, all its VM guest's data is reported and its ESX host status is OK. Any ideas on what could have happened?