The error message is coming from OpenSSL, not from Python. It looks like the handshake is failing with a problem in OpenSSL's internal elliptic curve crypto. It usually means that the server is sending handshake parameters or certs that the client cannot process. It could be a problem with key agreement with ECDHE or cert validation with an EC cert.

It's impossible to say what exactly is going wrong. I suggest that you start by debugging the issue with openssl s_client, Wireshark and gdb on the system.