Authenticated INVITE after 407 Proxy Authentication Required

[syco]

I have freeswitch with an authenticated gateway to a provider, routing calls through an outbound proxy.
There are multiple outbound proxies all under the same FQDN.
Occasionally, I guess when the FQDN ttl expires, the second INVITE with the authentication goes to a different proxy, causing the provider to see an initial attempt from a public ip and the authenticated attempt from a different public ip.

This might make it all more clear:

F.F.F.F is freeswitch
b.b.b.b is proxy 1
c.c.c.c is proxy 2
x.x.x.x is the provider

                 F.F.F.F                       b.b.b.b                       x.x.x.x                       c.c.c.c
          ──────────┬─────────          ──────────┬─────────          ──────────┬─────────          ──────────┬─────────
  01:10:10.038271   │        INVITE (SDP)         │                             │                             │
        +0.001389   │ ──────────────────────────> │                             │                             │
  01:10:10.039660   │     100 Giving it a try     │                             │                             │
        +0.001937   │ <────────────────────────── │                             │                             │
  01:10:10.041597   │                             │        INVITE (SDP)         │                             │
        +0.027705   │                             │ ──────────────────────────> │                             │
  01:10:10.069302   │                             │  407 Proxy Authentication R │                             │
        +0.000036   │                             │ <────────────────────────── │                             │
  01:10:10.069338   │                             │             ACK             │                             │
        +0.002714   │                             │ ──────────────────────────> │                             │
  01:10:10.072052   │  407 Proxy Authentication R │                             │                             │
        +0.000044   │ <────────────────────────── │                             │                             │
  01:10:10.072096   │             ACK             │                             │                             │
        +0.032171   │ ──────────────────────────> │                             │                             │
  01:10:10.104267   │                                      INVITE (SDP)                                       │
        +0.003914   │ ──────────────────────────────────────────────────────────────────────────────────────> │
  01:10:10.108181   │                                   100 Giving it a try                                   │
        +0.003612   │ <────────────────────────────────────────────────────────────────────────────────────── │
  01:10:10.111793   │                             │                             │        INVITE (SDP)         │
        +0.036972   │                             │                             │ <────────────────────────── │
  01:10:10.148765   │                             │                             │  100 trying -- your call is │
        +0.381662   │                             │                             │ ─────────────────────────── │
  01:10:10.530427   │                             │                             │  500 Internal Server Error  │
        +0.000107   │                             │                             │ ─────────────────────────── │
  01:10:10.530534   │                             │                             │             ACK             │
        +0.006302   │                             │                             │ <────────────────────────── │
  01:10:10.536836   │                 500 Internal Server Error                 │                             │
        +0.000064   │ <──────────────────────────────────────────────────────── │                             │
  01:10:10.536900   │                            ACK                            │                             │
                    │ ────────────────────────────────────────────────────────> │                             │

Expected behavior
There shouldn't be a dns resolution mid call, the second INVITE should go through the same proxy as the initial INVITE

Package version or git hash

• Version 1.10.11

Any thoughts on this?
Thanks