Strange Networking Issue VM/Reverse proxy

Version 2024.6.2
Web/Desktop

The vm running Vaultwarden have two network interfaces, one listening on the lan and another to an isolated network where only the reverse proxy have access.

192.168.0.x LAN
10.0.0.x SDN

The reverse proxy have access to both network and inside both network both machine are reachable, while pointing to the LAN address vaultwarden work just fine, while using the SDN address vaultwarden WORK but just partially i can log as admin using an admin token but the users login is not working.

It stop logging after:

vaultwarden | [vaultwarden::api::identity][INFO] User mail@mail.xx logged in successfully. IP: external IP
vaultwarden | [response][INFO] (login) POST /identity/connect/token => 200 OK

After that the web vault say “Unexpected Error” and give a timeout on:
POST https://subdomain.domain.xxx/identity/connect/token 504

EDIT:
Using GET it work and retrieve just a 404

anyone have any idea on what could be wrong?