Per https://discuss.elastic.co/t/ldaps-and-chain-of-certificates/250724 it's possible to get an SSL failure & diagnostic when the cipher requires certain key usage that is not permitted by the certificate.
To assist in such diagnostics, it would be of assistance to print out the ceritficate's KeyUsage and the session's Cipher suite in the message.
While we're doing that, the cert's ExtendedKeyUsage and session Protocol are probably worth including as well.