In my situation, I discovered that it was partly the theme being used. ThemeFusion — I get the plugin to work on the http side by leaving the fushion-builder plugin turned on, but I disable the fushion-builder in the ThemeFusion cPanel. (this effects all ThemeFushion Themes that come bundled with the Fushion-Builder)
The form builder will save with the Fushion-Builder disabled within the theme itself (leave the plugin turned on)
On the https side, you have to disable https, (plus doing all mentioned above) build your form, save it to whatever page, update the page, and then turn your https back on.
If you have to use a builder, I would suggest using js_composer to do all of the grunt work. (you can build the forms with js_composer plugin activated, but you can’t view the work in real time … You can save the forms though, and view them after you’ve saved the page.)