That was the right direction to solve the issue!
As I said on the first post, we are using :gun library for some internal process. The big issue looks like that when the library is connecting through a proxy server, it does not pass the SNI configuration to :ssl by default, and it should be passed through the options.
Also, at some point :gun splitted the transport_opts option into tls_opts and tcp_opts. Passing server_name_indication: 'HOSTNAME' inside tls_opts option made it work.
I have also added peer verification with a bundled CA cert as you suggested on the link.
Thanks a lot! <3
