This bug can happen only in theme in version below 1.7.
Since WordPress 4.7 there is bug in Redux framework that affects preview in Customizer.
It can be seen when you change few options without saving them. Earlier changed options will not be displayed, only 1 or 2 last changes will be displayed.
However when you save changes, all of them will appear on your site.
We plan to move away from Redux framework plugin in near future(I-II 2018) so it will be fixed then for sure, meanwhile you just have to keep that in mind.