enable HTTPS = can not connect to wordpress.com

Could you try some of the tips suggested here?
http://jetpack.me/support/getting-started-with-jetpack/troubleshooting-tips/

If that doesn’t help, could you post your site URL here so I can have a look?

If you want it to remain private, you can also contact us via this contact form:
http://jetpack.me/contact-support/

I still seem to be able to access your site via HTTP.

Could you let me know what your site and URL values are, under Settings > General in your dashboard? If you’d like to use HTTPS everywhere, you’ll need to switch to HTTPS there.

You could also use a plugin like this one to handle all redirections for you:
https://ww.wp.xz.cn/plugins/wordpress-https/

Once your site is full SSL, and if you’ve made the changes suggested in our support documentation, things should start working properly.

Let me know how it goes.

• http://www.freemag.one/ is still accessible via HTTP, though, while when visting http://www.artipa.com or http://www.dolezal.one I am automatically redirected to the HTTPS version of the site.

  Could you check the site settings to make sure they’re similar to the 2 other sites?

• http://www.artipa.com/

  Something seems wrong with your SSL Certificate configuration for this domain. Could you ask your hosting provider to take a look? You can forward them this error message:

  openssl s_client -connect artipa.com:443
  CONNECTED(00000003)
  depth=1 C = IL, O = StartCom Ltd., OU = Secure Digital Certificate Signing, CN = StartCom Class 1 Primary Intermediate Server CA
  verify error:num=20:unable to get local issuer certificate
  verify return:0

  It can also be useful to look at this page to learn more about the certificate:
  https://www.ssllabs.com/ssltest/analyze.html?d=artipa.com&latest

• http://www.dolezal.one/

  Could you try to change the $_SERVER['SERVER_PORT'] value, as suggested here, and let me know how it goes?
  http://jetpack.me/support/getting-started-with-jetpack/troubleshooting-tips/

I hope this helps.