Previewing MetaBoxes

The meta values are saved when you save the post as a draft. So they should be visible in the front end. How did you check that?

If you’re editing a published page and then click Preview then you can’t see the meta values unless you set “autosave” true for the meta box.

The thing here is WordPress auto saves post title and post content so you can preview them while edit (there must be a “save” action so you actually see the changes) and by default, Meta Box turns the autosave = off so you don’t see it. Setting “autosave” true fixes the problem.