HTTPS net::ERR_CERT_AUTHORITY_INVALID causing connection warning

[dhood]

With Chrome 64.0 on OSX I am unable to load codemontage.com unless I click through a warning similar to this one: https://qph.fs.quoracdn.net/main-qimg-b0bc2a8995fbfefeb5764fd3a3f33e4c

It says:

Your connection is not private
Attackers might be trying to steal your information from www.codemontage.com (for example, passwords, messages, or credit cards). Learn more
NET::ERR_CERT_AUTHORITY_INVALID
 
Automatically send some system information and page content to Google to help detect dangerous apps and sites. Privacy policy
This server could not prove that it is www.codemontage.com; its security certificate is not trusted by your computer's operating system. This may be caused by a misconfiguration or an attacker intercepting your connection.

Proceed to www.codemontage.com (unsafe)

If I disable the warning I can get through to the site via the bottom link but it's only available through the "advanced" options on the warning page so there are likely visitors that don't get to see the site.

The console gives the following output in case it's of any use:

This page is not secure (broken HTTPS).
Certificate error
There are issues with the site's certificate chain (net::ERR_CERT_AUTHORITY_INVALID).
View certificate
Secure connection
The connection to this site is encrypted and authenticated using TLS 1.2 (a strong protocol), ECDHE_RSA with P-256 (a strong key exchange), and AES_128_GCM (a strong cipher).

From what I understand this is something that needs to be changed on the hosting side of things, but it could be that it's caused by something unique to my machine setup.