[uzero]

It's issued by StartSSL and is valid on all the browsers I have tried the site on. Can you tell me what browser (and version) are you using?

[regecks]

https://www.ssllabs.com/ssltest/analyze.html?d=markopolojarv...

Intermediate certificate isn't sent by the server, which might be the issue.

[arbitrarilyHigh]

Not the person whom you asked, but I'm getting the same issue on up-to-date mobile Chrome on Note 3 standard build android 4.3

Surprisingly also getting the issue is the Samsung browser on the same android 4.3 phone.