WCF Service self-hosted not reachable from Intranet

Question

I've a WCF Service (self-hosted) inside a Windows Service running as LocalSystem. This Windows Service runs on a virtual environement in the cloud (OVH) This service is accessible through https with a real X509 certificate (from a CA). I use TransportWithMessageCredentials at transport level and username authentication at Message level.

My WCF client works fine from internet on https://wcfserver.domain.com. When I try to run my WCF client from intranet, he's not able to connect to https://wcfserver.domain.com.

I investiguate from intranet following tests:

• No WCF traces logged on server

• Internet explorer (network diag): the web service you try to reach is temporarly unavailable. The raison may be communication issues between Gateway and web service. Proxy or gateway returns 502 error. So I removed Timestamp in SOAP message but issue remains...

• Fiddler response is:

  Headers:
  HTTP/1.1 502 Fiddler - Connection Failed
  Date: Tue, 20 Sep 2016 16:14:07 GMT
  Content-Type: text/html; charset=UTF-8
  Connection: close
  Cache-Control: no-cache, must-revalidate
  Timestamp: 18:14:07.000
  
  Caching:
  Under RFC2616, HTTP/502 responses will not be cached regardless of what caching headers may be present.
  HTTP/1.1 Cache-Control Header is present: no-cache, must-revalidate
      no-cache: This response MUST NOT be reused without successful revalidation with the origin server.This response contains neither an ETAG nor a Last-Modified time. This will prevent a Conditional Revalidation of this response.
  

• I've also noticed that Web Service page is not accessible to https://wcfserver.domain.com, or with its public IP but I'm able to open it if I use local IP https://192.168.XXX.XXX (but I've to accept certificate warning manually)...

Any help or advices would be appreciated! :) I'm stuck!

Regards, François