I think I've narrowed down a problem with my marketpress on afcea-qp.org domain. I have product displaying at https://www.afcea-qp.org/store/products/2016-usmc-it-day-sponsorship/
It has 3 variations. The view more information doesn't work no matter whether I put information in the plain text field or not. Trying to add html content breaks it. I'm using Force HTTPS on the site to strip out any insecure content.
Is your plugin using some calls that are insecure and don't work when SSL is enforced?