I am calling SSL_connect(), checking the return value and printing any error:

const int res = SSL_connect(ssl);

ASSERT(1 == res, "SSL_connect() failed. error code (" << res << ") details: " << OpenSSLError(res));

the function printing details:

static inline std::string OpenSSLError()
{
    BIO *bio = BIO_new(BIO_s_mem());
    ERR_print_errors(bio);
    char *buf;
    size_t len = BIO_get_mem_data(bio, &buf);
    std::string ret(buf, len);
    BIO_free(bio);
    return ret;
}

is based on: /a/56752841/1107474

The assert just triggered with:

Assert failed. Msg: SSL_connect() failed. error code (-1) details:

but no details were provided.

Can anyone help with the error was?

Advise what I can change to ensure I catch the error details?

The code is surrounded with a mutex, so the issue wasn’t multithreading/corruption.