You should check the TLS settings and library (for example OpenSSL, GNUTLS) versions of the server. Your browser should tell you which version is used if you don't use the proxy.
The following error was encountered while trying to retrieve the URL: https://195.8.209.120/*Failed to establish a secure connection to 195.8.209.120The system returned:(92) Protocol error (TLS code: SQUID_ERR_SSL_HANDSHAKE)Handshake with SSL server failed: error:14077102:SSL routines:SSL23_GET_SERVER_HELLO:unsupported protocolThis proxy and the remote host failed to negotiate a mutually acceptable security settings for handling your request. It is possible that the remote host does not support secure connections, or the proxy is not satisfied with the host security credentials.
You should check the web server for the supported ciphers and TLS versions. If you navigate to it without the proxy, you can get into the menu showing it by clicking the lock icon in the address bar, then click ">" and click "more information". The should be some info under technical details. (Note: This explanation is Firefox only)