Assuming that version 3.6 is being used:
See: https://github.com/python/cpython/blob/3.6/Modules/_ssl.c#L3523-L3534
PySSL_BEGIN_ALLOW_THREADS_S(pw_info.thread_state);
r = SSL_CTX_check_private_key(self->ctx);
PySSL_END_ALLOW_THREADS_S(pw_info.thread_state);
if (r != 1) {
_setSSLError(NULL, 0, __FILE__, __LINE__);
goto error;
}
What it is saying is that SSL_CTX_check_private_key
failed; thus, the private key is not correct.
Reference to the likely version: