This error indicates that the Mendix runtime could not negotiate the HTTPS connection. I experienced this recently with a certificate signed by the GoDaddy root certificate authority, and I learned that was because Java doesn't natively trust this certificate authority (while most browsers do). Because the runtime doesn't trust GoDaddy, it doesn't trust any certificates signed by GoDaddy.
So, my solution was to import the site's certificate to the project. You can use the Chrome Developer Tools (F12) to download the certificate, then import it to your modeler or the Mendix cloud by following the documentation here.
Let us know how it goes!
Which certificates do I have to download and add to my project's Settings?
What I tried: In Chrome, on a SSL-certified site (https://bag.basisregistraties.overheid.nl), I click on the green lock in the URL-bar, click on site-settings, then on 'Settings' and on 'Privacy and Security' and then on 'Manage Certificates'. I tried my personal (first tab) which is the only one that requests a password. Tried the other certificates as well. I did add the ClientCertificates and ClientCertificatePasswords to the Project->settings but I kept getting the same Java errormessage about the PKIX path.
And I cannot download and save this one (F12->Security):