When SNMP v3 is used to discover a device that uses different security contexts for different instances of a MIB (in the same way that community string indexing is used for v1 or v2), the SNMP v3 user might not have access to the different security contexts.
If a device is discovered where access to different contexts is required, but access has not been granted to the user, discovery will gather less information and topology discovery might not be complete. A ScriptFailure node will be associated with the DeviceInfo for the DiscoveryAccess, with a message of the type, Failed to access vlan-1 (AuthorizationError), where vlan-1 is the name of the security context that discovery attempted to access.
To ensure discovery has full access, the user should be granted access to all of the contexts on the network device. For example, to grant access to all contexts to the group privgroup on a Cisco device with a recent version of IOS, you can use this configuration command:
snmp-server group privgroup v3 auth context vlan- match prefix
You should consult your device documentation or manufacturer for more details.