Added SSL cert for my Home Assistant gives curl ssl exceptions

Configuration
1

Running Hassbian and recently added SSL certificate for my setup with help of this tutorial: https://www.splitbrain.org/blog/2017-08/10-homeassistant_duckdns_letsencrypt

Problem I face now, some plugins give SSL errors… so I did some curl test to verify.

curl https://www.ophaalkalender.be -v

Gives

* Connected to www.ophaalkalender.be (81.246.112.169) port 443 (#0)
* ALPN, offering h2
* ALPN, offering http/1.1
* successfully set certificate verify locations:
*   CAfile: none
  CApath: /etc/ssl/certs
* TLSv1.3 (OUT), TLS handshake, Client hello (1):
* TLSv1.3 (IN), TLS handshake, Server hello (2):
* TLSv1.3 (OUT), TLS alert, protocol version (582):
* error:1425F102:SSL routines:ssl_choose_client_version:unsupported protocol
* Closing connection 0
curl: (35) error:1425F102:SSL routines:ssl_choose_client_version:unsupported protocol

And
curl --tlsv1.3 https://www.ophaalkalender.be -v

Gives

* Connected to www.ophaalkalender.be (81.246.112.169) port 443 (#0)
* ALPN, offering h2
* ALPN, offering http/1.1
* successfully set certificate verify locations:
*   CAfile: none
  CApath: /etc/ssl/certs
* TLSv1.3 (OUT), TLS handshake, Client hello (1):
* OpenSSL SSL_connect: SSL_ERROR_SYSCALL in connection to www.ophaalkalender.be:443 
* Closing connection 0
curl: (35) OpenSSL SSL_connect: SSL_ERROR_SYSCALL in connection to www.ophaalkalender.be:443

So no matter what I try with curl, I get some SSL error. It does change when I force tls v1.3 but the syscal error is also not good.
I’m no SSL expert so no clue where the actual problem can reside.