When I configure and ip6 route with outgoing interface, then dump the fib table, dump shows incorrect sw_if_index for the outgoing interface:

$ sudo service vpp restart

$ sudo vpp_api_test json

vat# ip_add_del_route 10::10/24 via 11::10/24 sw_if_index 1

vat# ip6_fib_dump

{
    "table": 0,
    "prefix": "10::10",
    "mask_length": 24,
    "path_count": 1,
    "weight": 16777216,
    "sw_if_index": 33554432,
    "is_local": 0,
    "is_drop": 0,
    "is_unreach": 0,
    "is_prohibit": 0,
    "next_hop_afi": 2,
    "next_hop": "11::10"
  },

Note the route does function correctly.

Also the IP4 version "ip_fib_dump" works as expected.