Apparently for some reason your Orion is getting another set of interface indexes via SNMP than is actually stored in interface fields in flows.
This is just fine in case you do not need to monitor the interface via Orion for status and other statistics, just for netflow data.
Do you see the VLAN interface when asking for list resources on that particular node in Orion node management?
Btw. you can always rename 'NTA Virtual Interface #xx' to something more meaningful by checking the interface in Orion node management, click Edit properties and change the name.