I ran into this exact same issue after upgrading from Basic Hosting to Plus Hosting on Bluehost and importing a new domain. I used the Free SSL from the WordPress Tools, and was getting the above error on my HTTPS version (although HTTP was fine).
I had to open three tickets within 24 hours with their support, finally on the third time it was resolved.
The first two support people said it was an issue with SiteLock not working with SSL, so Sitelock would need to be disabled. After waiting the 4-8 hours they said it would take, there was no change.
The second go around was the same, except after waiting a little, my site instead gave the “ERR_CERT_COMMON_NAME_INVALID” error. After clicking the “Proceed Anyway” button, my site actually redirected to a random, completely different site I didn’t own. Less than ideal…
The third support tech said the SSL cert needed to be uninstalled and reapplied, again with a 4-8 hour window. However, the site began working minutes after he said the changes were pending – so not really sure what’s going on over at Bluehost. I get the feeling many of the Level 1 Support Techs don’t have much technical expertise.