Misconfigured server certificate.
This means OpenSSL on your server isn't able to verify the host certificate.
There are a few reasons why this is happening. It could be that the host certificate is misconfigured, or this server's OpenSSL is using an outdated CA bundle.
Recommended next steps:
Verify that the host's SSL certificate is valid.
Contact your hosting support, show them the "full Error Log for debugging" below and share this link with them.
But how can they do it???