EDIT: Updated and re-tested on the new vlan model, simplified reproduce steps.

Steps to reproduce:
1. Setup configuration (or use provided config.json file):

1a. create Vlan sub-interface:
{"name": "GigabitEthernet0/8/0",
"vpp-vlan:sub-interfaces": {"sub-interface": [{"vlan-type": "802dot1q", "identifier": 1, "enabled": "false", "match": {"vlan-tagged": {"match-exact-tags": "true"}}, "tags": {"tag": [{"index": "0", "dot1q-tag": {"vlan-id": "100", "tag-type": "dot1q-types:s-vlan"}}, {"index": "1", "dot1q-tag": {"vlan-id": "any", "tag-type": "dot1q-types:c-vlan"}}]}}]}

1b. set super-interface and sub-interface states to "up":

1c. create any other interface (VxLan, TAP, vhost-user,...):
{"v3po:vxlan":

,
"type": "v3po:vxlan-tunnel",
"name": "vx_tunnel_test"}

2. restart Honeycomb and VPP

3. GET operational interface data:
HTTP ERROR 500; Problem accessing /restconf/operational/ietf-interfaces:interfaces-state
Reason: Server Error, Caused by: java.lang.IllegalStateException: Unexpected size of list: []. Single item expected

Full log included.